/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @fileoverview
*/
goog.provide('shaka.media.StreamingEngine');
goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.media.InitSegmentReference');
goog.require('shaka.media.ManifestParser');
goog.require('shaka.media.MediaSourceEngine');
goog.require('shaka.media.SegmentIterator');
goog.require('shaka.media.SegmentReference');
goog.require('shaka.media.SegmentPrefetch');
goog.require('shaka.net.Backoff');
goog.require('shaka.net.NetworkingEngine');
goog.require('shaka.util.BufferUtils');
goog.require('shaka.util.DelayedTick');
goog.require('shaka.util.Destroyer');
goog.require('shaka.util.Error');
goog.require('shaka.util.FakeEvent');
goog.require('shaka.util.IDestroyable');
goog.require('shaka.util.Id3Utils');
goog.require('shaka.util.LanguageUtils');
goog.require('shaka.util.ManifestParserUtils');
goog.require('shaka.util.MimeUtils');
goog.require('shaka.util.Mp4BoxParsers');
goog.require('shaka.util.Mp4Parser');
goog.require('shaka.util.Networking');
/**
* @summary Creates a Streaming Engine.
* The StreamingEngine is responsible for setting up the Manifest's Streams
* (i.e., for calling each Stream's createSegmentIndex() function), for
* downloading segments, for co-ordinating audio, video, and text buffering.
* The StreamingEngine provides an interface to switch between Streams, but it
* does not choose which Streams to switch to.
*
* The StreamingEngine does not need to be notified about changes to the
* Manifest's SegmentIndexes; however, it does need to be notified when new
* Variants are added to the Manifest.
*
* To start the StreamingEngine the owner must first call configure(), followed
* by one call to switchVariant(), one optional call to switchTextStream(), and
* finally a call to start(). After start() resolves, switch*() can be used
* freely.
*
* The owner must call seeked() each time the playhead moves to a new location
* within the presentation timeline; however, the owner may forego calling
* seeked() when the playhead moves outside the presentation timeline.
*
* @implements {shaka.util.IDestroyable}
*/
shaka.media.StreamingEngine = class {
/**
* @param {shaka.extern.Manifest} manifest
* @param {shaka.media.StreamingEngine.PlayerInterface} playerInterface
*/
constructor(manifest, playerInterface) {
/** @private {?shaka.media.StreamingEngine.PlayerInterface} */
this.playerInterface_ = playerInterface;
/** @private {?shaka.extern.Manifest} */
this.manifest_ = manifest;
/** @private {?shaka.extern.StreamingConfiguration} */
this.config_ = null;
/** @private {number} */
this.bufferingGoalScale_ = 1;
/** @private {?shaka.extern.Variant} */
this.currentVariant_ = null;
/** @private {?shaka.extern.Stream} */
this.currentTextStream_ = null;
/** @private {number} */
this.textStreamSequenceId_ = 0;
/** @private {boolean} */
this.parsedPrftEventRaised_ = false;
/**
* Maps a content type, e.g., 'audio', 'video', or 'text', to a MediaState.
*
* @private {!Map.<shaka.util.ManifestParserUtils.ContentType,
* !shaka.media.StreamingEngine.MediaState_>}
*/
this.mediaStates_ = new Map();
/**
* Set to true once the initial media states have been created.
*
* @private {boolean}
*/
this.startupComplete_ = false;
/**
* Used for delay and backoff of failure callbacks, so that apps do not
* retry instantly.
*
* @private {shaka.net.Backoff}
*/
this.failureCallbackBackoff_ = null;
/**
* Set to true on fatal error. Interrupts fetchAndAppend_().
*
* @private {boolean}
*/
this.fatalError_ = false;
/** @private {!shaka.util.Destroyer} */
this.destroyer_ = new shaka.util.Destroyer(() => this.doDestroy_());
/** @private {number} */
this.lastMediaSourceReset_ = Date.now() / 1000;
/**
* @private {!Map<shaka.extern.Stream, !shaka.media.SegmentPrefetch>}
*/
this.audioPrefetchMap_ = new Map();
/** @private {!shaka.extern.SpatialVideoInfo} */
this.spatialVideoInfo_ = {
projection: null,
hfov: null,
};
/** @private {number} */
this.playRangeStart_ = 0;
/** @private {number} */
this.playRangeEnd_ = Infinity;
}
/** @override */
destroy() {
return this.destroyer_.destroy();
}
/**
* @return {!Promise}
* @private
*/
async doDestroy_() {
const aborts = [];
for (const state of this.mediaStates_.values()) {
this.cancelUpdate_(state);
aborts.push(this.abortOperations_(state));
if (state.segmentPrefetch) {
state.segmentPrefetch.clearAll();
state.segmentPrefetch = null;
}
}
for (const prefetch of this.audioPrefetchMap_.values()) {
prefetch.clearAll();
}
await Promise.all(aborts);
this.mediaStates_.clear();
this.audioPrefetchMap_.clear();
this.playerInterface_ = null;
this.manifest_ = null;
this.config_ = null;
}
/**
* Called by the Player to provide an updated configuration any time it
* changes. Must be called at least once before start().
*
* @param {shaka.extern.StreamingConfiguration} config
*/
configure(config) {
this.config_ = config;
// Create separate parameters for backoff during streaming failure.
/** @type {shaka.extern.RetryParameters} */
const failureRetryParams = {
// The term "attempts" includes the initial attempt, plus all retries.
// In order to see a delay, there would have to be at least 2 attempts.
maxAttempts: Math.max(config.retryParameters.maxAttempts, 2),
baseDelay: config.retryParameters.baseDelay,
backoffFactor: config.retryParameters.backoffFactor,
fuzzFactor: config.retryParameters.fuzzFactor,
timeout: 0, // irrelevant
stallTimeout: 0, // irrelevant
connectionTimeout: 0, // irrelevant
};
// We don't want to ever run out of attempts. The application should be
// allowed to retry streaming infinitely if it wishes.
const autoReset = true;
this.failureCallbackBackoff_ =
new shaka.net.Backoff(failureRetryParams, autoReset);
const ContentType = shaka.util.ManifestParserUtils.ContentType;
// disable audio segment prefetch if this is now set
if (config.disableAudioPrefetch) {
const state = this.mediaStates_.get(ContentType.AUDIO);
if (state && state.segmentPrefetch) {
state.segmentPrefetch.clearAll();
state.segmentPrefetch = null;
}
for (const stream of this.audioPrefetchMap_.keys()) {
const prefetch = this.audioPrefetchMap_.get(stream);
prefetch.clearAll();
this.audioPrefetchMap_.delete(stream);
}
}
// disable text segment prefetch if this is now set
if (config.disableTextPrefetch) {
const state = this.mediaStates_.get(ContentType.TEXT);
if (state && state.segmentPrefetch) {
state.segmentPrefetch.clearAll();
state.segmentPrefetch = null;
}
}
// disable video segment prefetch if this is now set
if (config.disableVideoPrefetch) {
const state = this.mediaStates_.get(ContentType.VIDEO);
if (state && state.segmentPrefetch) {
state.segmentPrefetch.clearAll();
state.segmentPrefetch = null;
}
}
// Allow configuring the segment prefetch in middle of the playback.
for (const type of this.mediaStates_.keys()) {
const state = this.mediaStates_.get(type);
if (state.segmentPrefetch) {
state.segmentPrefetch.resetLimit(config.segmentPrefetchLimit);
if (!(config.segmentPrefetchLimit > 0)) {
// ResetLimit is still needed in this case,
// to abort existing prefetch operations.
state.segmentPrefetch.clearAll();
state.segmentPrefetch = null;
}
} else if (config.segmentPrefetchLimit > 0) {
state.segmentPrefetch = this.createSegmentPrefetch_(state.stream);
}
}
if (!config.disableAudioPrefetch) {
this.updatePrefetchMapForAudio_();
}
}
/**
* Applies a playback range. This will only affect non-live content.
*
* @param {number} playRangeStart
* @param {number} playRangeEnd
*/
applyPlayRange(playRangeStart, playRangeEnd) {
if (!this.manifest_.presentationTimeline.isLive()) {
this.playRangeStart_ = playRangeStart;
this.playRangeEnd_ = playRangeEnd;
}
}
/**
* Initialize and start streaming.
*
* By calling this method, StreamingEngine will start streaming the variant
* chosen by a prior call to switchVariant(), and optionally, the text stream
* chosen by a prior call to switchTextStream(). Once the Promise resolves,
* switch*() may be called freely.
*
* @param {!Map.<number, shaka.media.SegmentPrefetch>=} segmentPrefetchById
* If provided, segments prefetched for these streams will be used as needed
* during playback.
* @return {!Promise}
*/
async start(segmentPrefetchById) {
goog.asserts.assert(this.config_,
'StreamingEngine configure() must be called before init()!');
// Setup the initial set of Streams and then begin each update cycle.
await this.initStreams_(segmentPrefetchById || (new Map()));
this.destroyer_.ensureNotDestroyed();
shaka.log.debug('init: completed initial Stream setup');
this.startupComplete_ = true;
}
/**
* Get the current variant we are streaming. Returns null if nothing is
* streaming.
* @return {?shaka.extern.Variant}
*/
getCurrentVariant() {
return this.currentVariant_;
}
/**
* Get the text stream we are streaming. Returns null if there is no text
* streaming.
* @return {?shaka.extern.Stream}
*/
getCurrentTextStream() {
return this.currentTextStream_;
}
/**
* Start streaming text, creating a new media state.
*
* @param {shaka.extern.Stream} stream
* @return {!Promise}
* @private
*/
async loadNewTextStream_(stream) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
goog.asserts.assert(!this.mediaStates_.has(ContentType.TEXT),
'Should not call loadNewTextStream_ while streaming text!');
this.textStreamSequenceId_++;
const currentSequenceId = this.textStreamSequenceId_;
try {
// Clear MediaSource's buffered text, so that the new text stream will
// properly replace the old buffered text.
// TODO: Should this happen in unloadTextStream() instead?
await this.playerInterface_.mediaSourceEngine.clear(ContentType.TEXT);
} catch (error) {
if (this.playerInterface_) {
this.playerInterface_.onError(error);
}
}
const mimeType = shaka.util.MimeUtils.getFullType(
stream.mimeType, stream.codecs);
this.playerInterface_.mediaSourceEngine.reinitText(
mimeType, this.manifest_.sequenceMode, stream.external);
const textDisplayer =
this.playerInterface_.mediaSourceEngine.getTextDisplayer();
const streamText =
textDisplayer.isTextVisible() || this.config_.alwaysStreamText;
if (streamText && (this.textStreamSequenceId_ == currentSequenceId)) {
const state = this.createMediaState_(stream);
this.mediaStates_.set(ContentType.TEXT, state);
this.scheduleUpdate_(state, 0);
}
}
/**
* Stop fetching text stream when the user chooses to hide the captions.
*/
unloadTextStream() {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const state = this.mediaStates_.get(ContentType.TEXT);
if (state) {
this.cancelUpdate_(state);
this.abortOperations_(state).catch(() => {});
this.mediaStates_.delete(ContentType.TEXT);
}
this.currentTextStream_ = null;
}
/**
* Set trick play on or off.
* If trick play is on, related trick play streams will be used when possible.
* @param {boolean} on
*/
setTrickPlay(on) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
this.updateSegmentIteratorReverse_();
const mediaState = this.mediaStates_.get(ContentType.VIDEO);
if (!mediaState) {
return;
}
const stream = mediaState.stream;
if (!stream) {
return;
}
shaka.log.debug('setTrickPlay', on);
if (on) {
const trickModeVideo = stream.trickModeVideo;
if (!trickModeVideo) {
return; // Can't engage trick play.
}
const normalVideo = mediaState.restoreStreamAfterTrickPlay;
if (normalVideo) {
return; // Already in trick play.
}
shaka.log.debug('Engaging trick mode stream', trickModeVideo);
this.switchInternal_(trickModeVideo, /* clearBuffer= */ false,
/* safeMargin= */ 0, /* force= */ false);
mediaState.restoreStreamAfterTrickPlay = stream;
} else {
const normalVideo = mediaState.restoreStreamAfterTrickPlay;
if (!normalVideo) {
return;
}
shaka.log.debug('Restoring non-trick-mode stream', normalVideo);
mediaState.restoreStreamAfterTrickPlay = null;
this.switchInternal_(normalVideo, /* clearBuffer= */ true,
/* safeMargin= */ 0, /* force= */ false);
}
}
/**
* @param {shaka.extern.Variant} variant
* @param {boolean=} clearBuffer
* @param {number=} safeMargin
* @param {boolean=} force
* If true, reload the variant even if it did not change.
* @param {boolean=} adaptation
* If true, update the media state to indicate MediaSourceEngine should
* reset the timestamp offset to ensure the new track segments are correctly
* placed on the timeline.
*/
switchVariant(
variant, clearBuffer = false, safeMargin = 0, force = false,
adaptation = false) {
this.currentVariant_ = variant;
if (!this.startupComplete_) {
// The selected variant will be used in start().
return;
}
if (variant.video) {
this.switchInternal_(
variant.video, /* clearBuffer= */ clearBuffer,
/* safeMargin= */ safeMargin, /* force= */ force,
/* adaptation= */ adaptation);
}
if (variant.audio) {
this.switchInternal_(
variant.audio, /* clearBuffer= */ clearBuffer,
/* safeMargin= */ safeMargin, /* force= */ force,
/* adaptation= */ adaptation);
}
}
/**
* @param {shaka.extern.Stream} textStream
*/
async switchTextStream(textStream) {
this.currentTextStream_ = textStream;
if (!this.startupComplete_) {
// The selected text stream will be used in start().
return;
}
const ContentType = shaka.util.ManifestParserUtils.ContentType;
goog.asserts.assert(textStream && textStream.type == ContentType.TEXT,
'Wrong stream type passed to switchTextStream!');
// In HLS it is possible that the mimetype changes when the media
// playlist is downloaded, so it is necessary to have the updated data
// here.
if (!textStream.segmentIndex) {
await textStream.createSegmentIndex();
}
this.switchInternal_(
textStream, /* clearBuffer= */ true,
/* safeMargin= */ 0, /* force= */ false);
}
/** Reload the current text stream. */
reloadTextStream() {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const mediaState = this.mediaStates_.get(ContentType.TEXT);
if (mediaState) { // Don't reload if there's no text to begin with.
this.switchInternal_(
mediaState.stream, /* clearBuffer= */ true,
/* safeMargin= */ 0, /* force= */ true);
}
}
/**
* Switches to the given Stream. |stream| may be from any Variant.
*
* @param {shaka.extern.Stream} stream
* @param {boolean} clearBuffer
* @param {number} safeMargin
* @param {boolean} force
* If true, reload the text stream even if it did not change.
* @param {boolean=} adaptation
* If true, update the media state to indicate MediaSourceEngine should
* reset the timestamp offset to ensure the new track segments are correctly
* placed on the timeline.
* @private
*/
switchInternal_(stream, clearBuffer, safeMargin, force, adaptation) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const type = /** @type {!ContentType} */(stream.type);
const mediaState = this.mediaStates_.get(type);
if (!mediaState && stream.type == ContentType.TEXT) {
this.loadNewTextStream_(stream);
return;
}
goog.asserts.assert(mediaState, 'switch: expected mediaState to exist');
if (!mediaState) {
return;
}
if (mediaState.restoreStreamAfterTrickPlay) {
shaka.log.debug('switch during trick play mode', stream);
// Already in trick play mode, so stick with trick mode tracks if
// possible.
if (stream.trickModeVideo) {
// Use the trick mode stream, but revert to the new selection later.
mediaState.restoreStreamAfterTrickPlay = stream;
stream = stream.trickModeVideo;
shaka.log.debug('switch found trick play stream', stream);
} else {
// There is no special trick mode video for this stream!
mediaState.restoreStreamAfterTrickPlay = null;
shaka.log.debug('switch found no special trick play stream');
}
}
if (mediaState.stream == stream && !force) {
const streamTag = shaka.media.StreamingEngine.logPrefix_(mediaState);
shaka.log.debug('switch: Stream ' + streamTag + ' already active');
return;
}
if (this.audioPrefetchMap_.has(stream)) {
mediaState.segmentPrefetch = this.audioPrefetchMap_.get(stream);
} else if (mediaState.segmentPrefetch) {
mediaState.segmentPrefetch.switchStream(stream);
}
if (stream.type == ContentType.TEXT) {
// Mime types are allowed to change for text streams.
// Reinitialize the text parser, but only if we are going to fetch the
// init segment again.
const fullMimeType = shaka.util.MimeUtils.getFullType(
stream.mimeType, stream.codecs);
this.playerInterface_.mediaSourceEngine.reinitText(
fullMimeType, this.manifest_.sequenceMode, stream.external);
}
// Releases the segmentIndex of the old stream.
// Do not close segment indexes we are prefetching.
if (!this.audioPrefetchMap_.has(mediaState.stream)) {
if (mediaState.stream.closeSegmentIndex) {
mediaState.stream.closeSegmentIndex();
}
}
mediaState.stream = stream;
mediaState.segmentIterator = null;
mediaState.adaptation = !!adaptation;
const streamTag = shaka.media.StreamingEngine.logPrefix_(mediaState);
shaka.log.debug('switch: switching to Stream ' + streamTag);
if (clearBuffer) {
if (mediaState.clearingBuffer) {
// We are already going to clear the buffer, but make sure it is also
// flushed.
mediaState.waitingToFlushBuffer = true;
} else if (mediaState.performingUpdate) {
// We are performing an update, so we have to wait until it's finished.
// onUpdate_() will call clearBuffer_() when the update has finished.
// We need to save the safe margin because its value will be needed when
// clearing the buffer after the update.
mediaState.waitingToClearBuffer = true;
mediaState.clearBufferSafeMargin = safeMargin;
mediaState.waitingToFlushBuffer = true;
} else {
// Cancel the update timer, if any.
this.cancelUpdate_(mediaState);
// Clear right away.
this.clearBuffer_(mediaState, /* flush= */ true, safeMargin)
.catch((error) => {
if (this.playerInterface_) {
goog.asserts.assert(error instanceof shaka.util.Error,
'Wrong error type!');
this.playerInterface_.onError(error);
}
});
}
} else {
if (!mediaState.performingUpdate && !mediaState.updateTimer) {
this.scheduleUpdate_(mediaState, 0);
}
}
this.makeAbortDecision_(mediaState).catch((error) => {
if (this.playerInterface_) {
goog.asserts.assert(error instanceof shaka.util.Error,
'Wrong error type!');
this.playerInterface_.onError(error);
}
});
}
/**
* Decide if it makes sense to abort the current operation, and abort it if
* so.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @private
*/
async makeAbortDecision_(mediaState) {
// If the operation is completed, it will be set to null, and there's no
// need to abort the request.
if (!mediaState.operation) {
return;
}
const originalStream = mediaState.stream;
const originalOperation = mediaState.operation;
if (!originalStream.segmentIndex) {
// Create the new segment index so the time taken is accounted for when
// deciding whether to abort.
await originalStream.createSegmentIndex();
}
if (mediaState.operation != originalOperation) {
// The original operation completed while we were getting a segment index,
// so there's nothing to do now.
return;
}
if (mediaState.stream != originalStream) {
// The stream changed again while we were getting a segment index. We
// can't carry out this check, since another one might be in progress by
// now.
return;
}
goog.asserts.assert(mediaState.stream.segmentIndex,
'Segment index should exist by now!');
if (this.shouldAbortCurrentRequest_(mediaState)) {
shaka.log.info('Aborting current segment request.');
mediaState.operation.abort();
}
}
/**
* Returns whether we should abort the current request.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @return {boolean}
* @private
*/
shouldAbortCurrentRequest_(mediaState) {
goog.asserts.assert(mediaState.operation,
'Abort logic requires an ongoing operation!');
goog.asserts.assert(mediaState.stream && mediaState.stream.segmentIndex,
'Abort logic requires a segment index');
const presentationTime = this.playerInterface_.getPresentationTime();
const bufferEnd =
this.playerInterface_.mediaSourceEngine.bufferEnd(mediaState.type);
// The next segment to append from the current stream. This doesn't
// account for a pending network request and will likely be different from
// that since we just switched.
const timeNeeded = this.getTimeNeeded_(mediaState, presentationTime);
const index = mediaState.stream.segmentIndex.find(timeNeeded);
const newSegment =
index == null ? null : mediaState.stream.segmentIndex.get(index);
let newSegmentSize = newSegment ? newSegment.getSize() : null;
if (newSegment && !newSegmentSize) {
// compute approximate segment size using stream bandwidth
const duration = newSegment.getEndTime() - newSegment.getStartTime();
const bandwidth = mediaState.stream.bandwidth || 0;
// bandwidth is in bits per second, and the size is in bytes
newSegmentSize = duration * bandwidth / 8;
}
if (!newSegmentSize) {
return false;
}
// When switching, we'll need to download the init segment.
const init = newSegment.initSegmentReference;
if (init) {
newSegmentSize += init.getSize() || 0;
}
const bandwidthEstimate = this.playerInterface_.getBandwidthEstimate();
// The estimate is in bits per second, and the size is in bytes. The time
// remaining is in seconds after this calculation.
const timeToFetchNewSegment = (newSegmentSize * 8) / bandwidthEstimate;
// If the new segment can be finished in time without risking a buffer
// underflow, we should abort the old one and switch.
const bufferedAhead = (bufferEnd || 0) - presentationTime;
const safetyBuffer = Math.max(
this.manifest_.minBufferTime || 0,
this.config_.rebufferingGoal);
const safeBufferedAhead = bufferedAhead - safetyBuffer;
if (timeToFetchNewSegment < safeBufferedAhead) {
return true;
}
// If the thing we want to switch to will be done more quickly than what
// we've got in progress, we should abort the old one and switch.
const bytesRemaining = mediaState.operation.getBytesRemaining();
if (bytesRemaining > newSegmentSize) {
return true;
}
// Otherwise, complete the operation in progress.
return false;
}
/**
* Notifies the StreamingEngine that the playhead has moved to a valid time
* within the presentation timeline.
*/
seeked() {
if (!this.playerInterface_) {
// Already destroyed.
return;
}
const presentationTime = this.playerInterface_.getPresentationTime();
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const newTimeIsBuffered = (type) => {
return this.playerInterface_.mediaSourceEngine.isBuffered(
type, presentationTime);
};
let streamCleared = false;
for (const type of this.mediaStates_.keys()) {
const mediaState = this.mediaStates_.get(type);
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
let segment = null;
if (mediaState.segmentIterator) {
segment = mediaState.segmentIterator.current();
}
// Only reset the iterator if we seek outside the current segment.
if (!segment || segment.startTime > presentationTime ||
segment.endTime < presentationTime) {
mediaState.segmentIterator = null;
}
if (!newTimeIsBuffered(type)) {
const bufferEnd =
this.playerInterface_.mediaSourceEngine.bufferEnd(type);
const somethingBuffered = bufferEnd != null;
// Don't clear the buffer unless something is buffered. This extra
// check prevents extra, useless calls to clear the buffer.
if (somethingBuffered || mediaState.performingUpdate) {
this.forceClearBuffer_(mediaState);
streamCleared = true;
}
// If there is an operation in progress, stop it now.
if (mediaState.operation) {
mediaState.operation.abort();
shaka.log.debug(logPrefix, 'Aborting operation due to seek');
mediaState.operation = null;
}
// The pts has shifted from the seek, invalidating captions currently
// in the text buffer. Thus, clear and reset the caption parser.
if (type === ContentType.TEXT) {
this.playerInterface_.mediaSourceEngine.resetCaptionParser();
}
// Mark the media state as having seeked, so that the new buffers know
// that they will need to be at a new position (for sequence mode).
mediaState.seeked = true;
}
}
if (!streamCleared) {
shaka.log.debug(
'(all): seeked: buffered seek: presentationTime=' + presentationTime);
}
}
/**
* Clear the buffer for a given stream. Unlike clearBuffer_, this will handle
* cases where a MediaState is performing an update. After this runs, the
* MediaState will have a pending update.
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @private
*/
forceClearBuffer_(mediaState) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
if (mediaState.clearingBuffer) {
// We're already clearing the buffer, so we don't need to clear the
// buffer again.
shaka.log.debug(logPrefix, 'clear: already clearing the buffer');
return;
}
if (mediaState.waitingToClearBuffer) {
// May not be performing an update, but an update will still happen.
// See: https://github.com/shaka-project/shaka-player/issues/334
shaka.log.debug(logPrefix, 'clear: already waiting');
return;
}
if (mediaState.performingUpdate) {
// We are performing an update, so we have to wait until it's finished.
// onUpdate_() will call clearBuffer_() when the update has finished.
shaka.log.debug(logPrefix, 'clear: currently updating');
mediaState.waitingToClearBuffer = true;
// We can set the offset to zero to remember that this was a call to
// clearAllBuffers.
mediaState.clearBufferSafeMargin = 0;
return;
}
const type = mediaState.type;
if (this.playerInterface_.mediaSourceEngine.bufferStart(type) == null) {
// Nothing buffered.
shaka.log.debug(logPrefix, 'clear: nothing buffered');
if (mediaState.updateTimer == null) {
// Note: an update cycle stops when we buffer to the end of the
// presentation, or when we raise an error.
this.scheduleUpdate_(mediaState, 0);
}
return;
}
// An update may be scheduled, but we can just cancel it and clear the
// buffer right away. Note: clearBuffer_() will schedule the next update.
shaka.log.debug(logPrefix, 'clear: handling right now');
this.cancelUpdate_(mediaState);
this.clearBuffer_(mediaState, /* flush= */ false, 0).catch((error) => {
if (this.playerInterface_) {
goog.asserts.assert(error instanceof shaka.util.Error,
'Wrong error type!');
this.playerInterface_.onError(error);
}
});
}
/**
* Initializes the initial streams and media states. This will schedule
* updates for the given types.
*
* @param {!Map.<number, shaka.media.SegmentPrefetch>} segmentPrefetchById
* @return {!Promise}
* @private
*/
async initStreams_(segmentPrefetchById) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
goog.asserts.assert(this.config_,
'StreamingEngine configure() must be called before init()!');
if (!this.currentVariant_) {
shaka.log.error('init: no Streams chosen');
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.STREAMING,
shaka.util.Error.Code.STREAMING_ENGINE_STARTUP_INVALID_STATE);
}
/**
* @type {!Map.<shaka.util.ManifestParserUtils.ContentType,
* shaka.extern.Stream>}
*/
const streamsByType = new Map();
/** @type {!Set.<shaka.extern.Stream>} */
const streams = new Set();
if (this.currentVariant_.audio) {
streamsByType.set(ContentType.AUDIO, this.currentVariant_.audio);
streams.add(this.currentVariant_.audio);
}
if (this.currentVariant_.video) {
streamsByType.set(ContentType.VIDEO, this.currentVariant_.video);
streams.add(this.currentVariant_.video);
}
if (this.currentTextStream_) {
streamsByType.set(ContentType.TEXT, this.currentTextStream_);
streams.add(this.currentTextStream_);
}
// Init MediaSourceEngine.
const mediaSourceEngine = this.playerInterface_.mediaSourceEngine;
await mediaSourceEngine.init(streamsByType,
this.manifest_.sequenceMode,
this.manifest_.type,
this.manifest_.ignoreManifestTimestampsInSegmentsMode,
);
this.destroyer_.ensureNotDestroyed();
this.updateDuration();
for (const type of streamsByType.keys()) {
const stream = streamsByType.get(type);
if (!this.mediaStates_.has(type)) {
const mediaState = this.createMediaState_(stream);
if (segmentPrefetchById.has(stream.id)) {
const segmentPrefetch = segmentPrefetchById.get(stream.id);
segmentPrefetch.replaceFetchDispatcher(
(reference, stream, streamDataCallback) => {
return this.dispatchFetch_(
reference, stream, streamDataCallback);
});
mediaState.segmentPrefetch = segmentPrefetch;
}
this.mediaStates_.set(type, mediaState);
this.scheduleUpdate_(mediaState, 0);
}
}
}
/**
* Creates a media state.
*
* @param {shaka.extern.Stream} stream
* @return {shaka.media.StreamingEngine.MediaState_}
* @private
*/
createMediaState_(stream) {
return /** @type {shaka.media.StreamingEngine.MediaState_} */ ({
stream,
type: stream.type,
segmentIterator: null,
segmentPrefetch: this.createSegmentPrefetch_(stream),
lastSegmentReference: null,
lastInitSegmentReference: null,
lastTimestampOffset: null,
lastAppendWindowStart: null,
lastAppendWindowEnd: null,
restoreStreamAfterTrickPlay: null,
endOfStream: false,
performingUpdate: false,
updateTimer: null,
waitingToClearBuffer: false,
clearBufferSafeMargin: 0,
waitingToFlushBuffer: false,
clearingBuffer: false,
// The playhead might be seeking on startup, if a start time is set, so
// start "seeked" as true.
seeked: true,
recovering: false,
hasError: false,
operation: null,
});
}
/**
* Creates a media state.
*
* @param {shaka.extern.Stream} stream
* @return {shaka.media.SegmentPrefetch | null}
* @private
*/
createSegmentPrefetch_(stream) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
if (stream.type === ContentType.VIDEO &&
this.config_.disableVideoPrefetch) {
return null;
}
if (stream.type === ContentType.AUDIO &&
this.config_.disableAudioPrefetch) {
return null;
}
const MimeUtils = shaka.util.MimeUtils;
const CEA608_MIME = MimeUtils.CEA608_CLOSED_CAPTION_MIMETYPE;
const CEA708_MIME = MimeUtils.CEA708_CLOSED_CAPTION_MIMETYPE;
if (stream.type === ContentType.TEXT &&
(stream.mimeType == CEA608_MIME || stream.mimeType == CEA708_MIME)) {
return null;
}
if (stream.type === ContentType.TEXT &&
this.config_.disableTextPrefetch) {
return null;
}
if (this.audioPrefetchMap_.has(stream)) {
return this.audioPrefetchMap_.get(stream);
}
const type = /** @type {!shaka.util.ManifestParserUtils.ContentType} */
(stream.type);
const mediaState = this.mediaStates_.get(type);
const currentSegmentPrefetch = mediaState && mediaState.segmentPrefetch;
if (currentSegmentPrefetch &&
stream === currentSegmentPrefetch.getStream()) {
return currentSegmentPrefetch;
}
if (this.config_.segmentPrefetchLimit > 0) {
return new shaka.media.SegmentPrefetch(
this.config_.segmentPrefetchLimit,
stream,
(reference, stream, streamDataCallback) => {
return this.dispatchFetch_(reference, stream, streamDataCallback);
},
);
}
return null;
}
/**
* Populates the prefetch map depending on the configuration
* @private
*/
updatePrefetchMapForAudio_() {
const prefetchLimit = this.config_.segmentPrefetchLimit;
const prefetchLanguages = this.config_.prefetchAudioLanguages;
const LanguageUtils = shaka.util.LanguageUtils;
for (const variant of this.manifest_.variants) {
if (!variant.audio) {
continue;
}
if (this.audioPrefetchMap_.has(variant.audio)) {
// if we already have a segment prefetch,
// update it's prefetch limit and if the new limit isn't positive,
// remove the segment prefetch from our prefetch map.
const prefetch = this.audioPrefetchMap_.get(variant.audio);
prefetch.resetLimit(prefetchLimit);
if (!(prefetchLimit > 0) ||
!prefetchLanguages.some(
(lang) => LanguageUtils.areLanguageCompatible(
variant.audio.language, lang))
) {
const type = /** @type {!shaka.util.ManifestParserUtils.ContentType}*/
(variant.audio.type);
const mediaState = this.mediaStates_.get(type);
const currentSegmentPrefetch = mediaState &&
mediaState.segmentPrefetch;
// if this prefetch isn't the current one, we want to clear it
if (prefetch !== currentSegmentPrefetch) {
prefetch.clearAll();
}
this.audioPrefetchMap_.delete(variant.audio);
}
continue;
}
// don't try to create a new segment prefetch if the limit isn't positive.
if (prefetchLimit <= 0) {
continue;
}
// only create a segment prefetch if its language is configured
// to be prefetched
if (!prefetchLanguages.some(
(lang) => LanguageUtils.areLanguageCompatible(
variant.audio.language, lang))) {
continue;
}
// use the helper to create a segment prefetch to ensure that existing
// objects are reused.
const segmentPrefetch = this.createSegmentPrefetch_(variant.audio);
// if a segment prefetch wasn't created, skip the rest
if (!segmentPrefetch) {
continue;
}
if (!variant.audio.segmentIndex) {
variant.audio.createSegmentIndex();
}
this.audioPrefetchMap_.set(variant.audio, segmentPrefetch);
}
}
/**
* Sets the MediaSource's duration.
*/
updateDuration() {
const duration = this.manifest_.presentationTimeline.getDuration();
if (duration < Infinity) {
this.playerInterface_.mediaSourceEngine.setDuration(duration);
} else {
// To set the media source live duration as Infinity
// If infiniteLiveStreamDuration as true
const duration =
this.config_.infiniteLiveStreamDuration ? Infinity : Math.pow(2, 32);
// Not all platforms support infinite durations, so set a finite duration
// so we can append segments and so the user agent can seek.
this.playerInterface_.mediaSourceEngine.setDuration(duration);
}
}
/**
* Called when |mediaState|'s update timer has expired.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @suppress {suspiciousCode} The compiler assumes that updateTimer can't
* change during the await, and so complains about the null check.
* @private
*/
async onUpdate_(mediaState) {
this.destroyer_.ensureNotDestroyed();
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
// Sanity check.
goog.asserts.assert(
!mediaState.performingUpdate && (mediaState.updateTimer != null),
logPrefix + ' unexpected call to onUpdate_()');
if (mediaState.performingUpdate || (mediaState.updateTimer == null)) {
return;
}
goog.asserts.assert(
!mediaState.clearingBuffer, logPrefix +
' onUpdate_() should not be called when clearing the buffer');
if (mediaState.clearingBuffer) {
return;
}
mediaState.updateTimer = null;
// Handle pending buffer clears.
if (mediaState.waitingToClearBuffer) {
// Note: clearBuffer_() will schedule the next update.
shaka.log.debug(logPrefix, 'skipping update and clearing the buffer');
await this.clearBuffer_(
mediaState, mediaState.waitingToFlushBuffer,
mediaState.clearBufferSafeMargin);
return;
}
// Make sure the segment index exists. If not, create the segment index.
if (!mediaState.stream.segmentIndex) {
const thisStream = mediaState.stream;
await mediaState.stream.createSegmentIndex();
if (thisStream != mediaState.stream) {
// We switched streams while in the middle of this async call to
// createSegmentIndex. Abandon this update and schedule a new one if
// there's not already one pending.
// Releases the segmentIndex of the old stream.
if (thisStream.closeSegmentIndex) {
goog.asserts.assert(!mediaState.stream.segmentIndex,
'mediastate.stream should not have segmentIndex yet.');
thisStream.closeSegmentIndex();
}
if (!mediaState.performingUpdate && !mediaState.updateTimer) {
this.scheduleUpdate_(mediaState, 0);
}
return;
}
}
// Update the MediaState.
try {
const delay = this.update_(mediaState);
if (delay != null) {
this.scheduleUpdate_(mediaState, delay);
mediaState.hasError = false;
}
} catch (error) {
await this.handleStreamingError_(mediaState, error);
return;
}
const mediaStates = Array.from(this.mediaStates_.values());
// Check if we've buffered to the end of the presentation. We delay adding
// the audio and video media states, so it is possible for the text stream
// to be the only state and buffer to the end. So we need to wait until we
// have completed startup to determine if we have reached the end.
if (this.startupComplete_ &&
mediaStates.every((ms) => ms.endOfStream)) {
shaka.log.v1(logPrefix, 'calling endOfStream()...');
await this.playerInterface_.mediaSourceEngine.endOfStream();
this.destroyer_.ensureNotDestroyed();
// If the media segments don't reach the end, then we need to update the
// timeline duration to match the final media duration to avoid
// buffering forever at the end.
// We should only do this if the duration needs to shrink.
// Growing it by less than 1ms can actually cause buffering on
// replay, as in https://github.com/shaka-project/shaka-player/issues/979
// On some platforms, this can spuriously be 0, so ignore this case.
// https://github.com/shaka-project/shaka-player/issues/1967,
const duration = this.playerInterface_.mediaSourceEngine.getDuration();
if (duration != 0 &&
duration < this.manifest_.presentationTimeline.getDuration()) {
this.manifest_.presentationTimeline.setDuration(duration);
}
}
}
/**
* Updates the given MediaState.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @return {?number} The number of seconds to wait until updating again or
* null if another update does not need to be scheduled.
* @private
*/
update_(mediaState) {
goog.asserts.assert(this.manifest_, 'manifest_ should not be null');
goog.asserts.assert(this.config_, 'config_ should not be null');
const ContentType = shaka.util.ManifestParserUtils.ContentType;
// Do not schedule update for closed captions text mediastate, since closed
// captions are embedded in video streams.
if (shaka.media.StreamingEngine.isEmbeddedText_(mediaState)) {
this.playerInterface_.mediaSourceEngine.setSelectedClosedCaptionId(
mediaState.stream.originalId || '');
return null;
} else if (mediaState.type == ContentType.TEXT) {
// Disable embedded captions if not desired (e.g. if transitioning from
// embedded to not-embedded captions).
this.playerInterface_.mediaSourceEngine.clearSelectedClosedCaptionId();
}
if (!this.playerInterface_.mediaSourceEngine.isStreamingAllowed() &&
mediaState.type != ContentType.TEXT) {
// It is not allowed to add segments yet, so we schedule an update to
// check again later. So any prediction we make now could be terribly
// invalid soon.
return this.config_.updateIntervalSeconds / 2;
}
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
// Compute how far we've buffered ahead of the playhead.
const presentationTime = this.playerInterface_.getPresentationTime();
if (mediaState.type === ContentType.AUDIO) {
// evict all prefetched segments that are before the presentationTime
for (const stream of this.audioPrefetchMap_.keys()) {
const prefetch = this.audioPrefetchMap_.get(stream);
prefetch.evict(presentationTime, /* clearInitSegments= */ true);
prefetch.prefetchSegmentsByTime(presentationTime);
}
}
// Get the next timestamp we need.
const timeNeeded = this.getTimeNeeded_(mediaState, presentationTime);
shaka.log.v2(logPrefix, 'timeNeeded=' + timeNeeded);
// Get the amount of content we have buffered, accounting for drift. This
// is only used to determine if we have meet the buffering goal. This
// should be the same method that PlayheadObserver uses.
const bufferedAhead =
this.playerInterface_.mediaSourceEngine.bufferedAheadOf(
mediaState.type, presentationTime);
shaka.log.v2(logPrefix,
'update_:',
'presentationTime=' + presentationTime,
'bufferedAhead=' + bufferedAhead);
const unscaledBufferingGoal = Math.max(
this.manifest_.minBufferTime || 0,
this.config_.rebufferingGoal,
this.config_.bufferingGoal);
const scaledBufferingGoal = Math.max(1,
unscaledBufferingGoal * this.bufferingGoalScale_);
// Check if we've buffered to the end of the presentation.
const timeUntilEnd =
this.manifest_.presentationTimeline.getDuration() - timeNeeded;
const oneMicrosecond = 1e-6;
const bufferEnd =
this.playerInterface_.mediaSourceEngine.bufferEnd(mediaState.type);
if (timeUntilEnd < oneMicrosecond && !!bufferEnd) {
// We shouldn't rebuffer if the playhead is close to the end of the
// presentation.
shaka.log.debug(logPrefix, 'buffered to end of presentation');
mediaState.endOfStream = true;
if (mediaState.type == ContentType.VIDEO) {
// Since the text stream of CEA closed captions doesn't have update
// timer, we have to set the text endOfStream based on the video
// stream's endOfStream state.
const textState = this.mediaStates_.get(ContentType.TEXT);
if (textState &&
shaka.media.StreamingEngine.isEmbeddedText_(textState)) {
textState.endOfStream = true;
}
}
return null;
}
mediaState.endOfStream = false;
// If we've buffered to the buffering goal then schedule an update.
if (bufferedAhead >= scaledBufferingGoal) {
shaka.log.v2(logPrefix, 'buffering goal met');
// Do not try to predict the next update. Just poll according to
// configuration (seconds). The playback rate can change at any time, so
// any prediction we make now could be terribly invalid soon.
return this.config_.updateIntervalSeconds / 2;
}
const reference = this.getSegmentReferenceNeeded_(
mediaState, presentationTime, bufferEnd);
if (!reference) {
// The segment could not be found, does not exist, or is not available.
// In any case just try again... if the manifest is incomplete or is not
// being updated then we'll idle forever; otherwise, we'll end up getting
// a SegmentReference eventually.
return this.config_.updateIntervalSeconds;
}
// Do not let any one stream get far ahead of any other.
let minTimeNeeded = Infinity;
const mediaStates = Array.from(this.mediaStates_.values());
for (const otherState of mediaStates) {
// Do not consider embedded captions in this calculation. It could lead
// to hangs in streaming.
if (shaka.media.StreamingEngine.isEmbeddedText_(otherState)) {
continue;
}
// If there is no next segment, ignore this stream. This happens with
// text when there's a Period with no text in it.
if (otherState.segmentIterator && !otherState.segmentIterator.current()) {
continue;
}
const timeNeeded = this.getTimeNeeded_(otherState, presentationTime);
minTimeNeeded = Math.min(minTimeNeeded, timeNeeded);
}
const maxSegmentDuration =
this.manifest_.presentationTimeline.getMaxSegmentDuration();
const maxRunAhead = maxSegmentDuration *
shaka.media.StreamingEngine.MAX_RUN_AHEAD_SEGMENTS_;
if (timeNeeded >= minTimeNeeded + maxRunAhead) {
// Wait and give other media types time to catch up to this one.
// For example, let video buffering catch up to audio buffering before
// fetching another audio segment.
shaka.log.v2(logPrefix, 'waiting for other streams to buffer');
return this.config_.updateIntervalSeconds;
}
if (mediaState.segmentPrefetch && mediaState.segmentIterator &&
!this.audioPrefetchMap_.has(mediaState.stream)) {
mediaState.segmentPrefetch.evict(presentationTime);
mediaState.segmentPrefetch.prefetchSegmentsByTime(reference.startTime);
}
const p = this.fetchAndAppend_(mediaState, presentationTime, reference);
p.catch(() => {}); // TODO(#1993): Handle asynchronous errors.
return null;
}
/**
* Gets the next timestamp needed. Returns the playhead's position if the
* buffer is empty; otherwise, returns the time at which the last segment
* appended ends.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @param {number} presentationTime
* @return {number} The next timestamp needed.
* @private
*/
getTimeNeeded_(mediaState, presentationTime) {
// Get the next timestamp we need. We must use |lastSegmentReference|
// to determine this and not the actual buffer for two reasons:
// 1. Actual segments end slightly before their advertised end times, so
// the next timestamp we need is actually larger than |bufferEnd|.
// 2. There may be drift (the timestamps in the segments are ahead/behind
// of the timestamps in the manifest), but we need drift-free times
// when comparing times against the presentation timeline.
if (!mediaState.lastSegmentReference) {
return presentationTime;
}
return mediaState.lastSegmentReference.endTime;
}
/**
* Gets the SegmentReference of the next segment needed.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @param {number} presentationTime
* @param {?number} bufferEnd
* @return {shaka.media.SegmentReference} The SegmentReference of the
* next segment needed. Returns null if a segment could not be found, does
* not exist, or is not available.
* @private
*/
getSegmentReferenceNeeded_(mediaState, presentationTime, bufferEnd) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
goog.asserts.assert(
mediaState.stream.segmentIndex,
'segment index should have been generated already');
if (mediaState.segmentIterator) {
// Something is buffered from the same Stream. Use the current position
// in the segment index. This is updated via next() after each segment is
// appended.
return mediaState.segmentIterator.current();
} else if (mediaState.lastSegmentReference || bufferEnd) {
// Something is buffered from another Stream.
const time = mediaState.lastSegmentReference ?
mediaState.lastSegmentReference.endTime :
bufferEnd;
goog.asserts.assert(time != null, 'Should have a time to search');
shaka.log.v1(
logPrefix, 'looking up segment from new stream endTime:', time);
const reverse = this.playerInterface_.getPlaybackRate() < 0;
mediaState.segmentIterator =
mediaState.stream.segmentIndex.getIteratorForTime(
time, /* allowNonIndepedent= */ false, reverse);
const ref = mediaState.segmentIterator &&
mediaState.segmentIterator.next().value;
if (ref == null) {
shaka.log.warning(logPrefix, 'cannot find segment', 'endTime:', time);
}
return ref;
} else {
// Nothing is buffered. Start at the playhead time.
// If there's positive drift then we need to adjust the lookup time, and
// may wind up requesting the previous segment to be safe.
// inaccurateManifestTolerance should be 0 for low latency streaming.
const inaccurateTolerance = this.config_.inaccurateManifestTolerance;
const lookupTime = Math.max(presentationTime - inaccurateTolerance, 0);
shaka.log.v1(logPrefix, 'looking up segment',
'lookupTime:', lookupTime,
'presentationTime:', presentationTime);
const reverse = this.playerInterface_.getPlaybackRate() < 0;
let ref = null;
if (inaccurateTolerance) {
mediaState.segmentIterator =
mediaState.stream.segmentIndex.getIteratorForTime(
lookupTime, /* allowNonIndepedent= */ false, reverse);
ref = mediaState.segmentIterator &&
mediaState.segmentIterator.next().value;
}
if (!ref) {
// If we can't find a valid segment with the drifted time, look for a
// segment with the presentation time.
mediaState.segmentIterator =
mediaState.stream.segmentIndex.getIteratorForTime(
presentationTime, /* allowNonIndepedent= */ false, reverse);
ref = mediaState.segmentIterator &&
mediaState.segmentIterator.next().value;
}
if (ref == null) {
shaka.log.warning(logPrefix, 'cannot find segment',
'lookupTime:', lookupTime,
'presentationTime:', presentationTime);
}
return ref;
}
}
/**
* Fetches and appends the given segment. Sets up the given MediaState's
* associated SourceBuffer and evicts segments if either are required
* beforehand. Schedules another update after completing successfully.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @param {number} presentationTime
* @param {!shaka.media.SegmentReference} reference
* @private
*/
async fetchAndAppend_(mediaState, presentationTime, reference) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const StreamingEngine = shaka.media.StreamingEngine;
const logPrefix = StreamingEngine.logPrefix_(mediaState);
shaka.log.v1(logPrefix,
'fetchAndAppend_:',
'presentationTime=' + presentationTime,
'reference.startTime=' + reference.startTime,
'reference.endTime=' + reference.endTime);
// Subtlety: The playhead may move while asynchronous update operations are
// in progress, so we should avoid calling playhead.getTime() in any
// callbacks. Furthermore, switch() or seeked() may be called at any time,
// so we store the old iterator. This allows the mediaState to change and
// we'll update the old iterator.
const stream = mediaState.stream;
const iter = mediaState.segmentIterator;
mediaState.performingUpdate = true;
try {
if (reference.getStatus() ==
shaka.media.SegmentReference.Status.MISSING) {
throw new shaka.util.Error(
shaka.util.Error.Severity.RECOVERABLE,
shaka.util.Error.Category.NETWORK,
shaka.util.Error.Code.SEGMENT_MISSING);
}
await this.initSourceBuffer_(mediaState, reference);
this.destroyer_.ensureNotDestroyed();
if (this.fatalError_) {
return;
}
shaka.log.v2(logPrefix, 'fetching segment');
const isMP4 = stream.mimeType == 'video/mp4' ||
stream.mimeType == 'audio/mp4';
const isReadableStreamSupported = window.ReadableStream;
// Enable MP4 low latency streaming with ReadableStream chunked data.
// And only for DASH and HLS with byterange optimization.
if (this.config_.lowLatencyMode && isReadableStreamSupported && isMP4 &&
(this.manifest_.type != shaka.media.ManifestParser.HLS ||
reference.hasByterangeOptimization())) {
let remaining = new Uint8Array(0);
let processingResult = false;
let callbackCalled = false;
let streamDataCallbackError;
const streamDataCallback = async (data) => {
if (processingResult) {
// If the fallback result processing was triggered, don't also
// append the buffer here. In theory this should never happen,
// but it does on some older TVs.
return;
}
callbackCalled = true;
this.destroyer_.ensureNotDestroyed();
if (this.fatalError_) {
return;
}
try {
// Append the data with complete boxes.
// Every time streamDataCallback gets called, append the new data
// to the remaining data.
// Find the last fully completed Mdat box, and slice the data into
// two parts: the first part with completed Mdat boxes, and the
// second part with an incomplete box.
// Append the first part, and save the second part as remaining
// data, and handle it with the next streamDataCallback call.
remaining = this.concatArray_(remaining, data);
let sawMDAT = false;
let offset = 0;
new shaka.util.Mp4Parser()
.box('mdat', (box) => {
offset = box.size + box.start;
sawMDAT = true;
})
.parse(remaining, /* partialOkay= */ false,
/* isChunkedData= */ true);
if (sawMDAT) {
const dataToAppend = remaining.subarray(0, offset);
remaining = remaining.subarray(offset);
await this.append_(
mediaState, presentationTime, stream, reference, dataToAppend,
/* isChunkedData= */ true);
if (mediaState.segmentPrefetch && mediaState.segmentIterator) {
mediaState.segmentPrefetch.prefetchSegmentsByTime(
reference.startTime, /* skipFirst= */ true);
}
}
} catch (error) {
streamDataCallbackError = error;
}
};
const result =
await this.fetch_(mediaState, reference, streamDataCallback);
if (streamDataCallbackError) {
throw streamDataCallbackError;
}
if (!callbackCalled) {
// In some environments, we might be forced to use network plugins
// that don't support streamDataCallback. In those cases, as a
// fallback, append the buffer here.
processingResult = true;
this.destroyer_.ensureNotDestroyed();
if (this.fatalError_) {
return;
}
// If the text stream gets switched between fetch_() and append_(),
// the new text parser is initialized, but the new init segment is
// not fetched yet. That would cause an error in
// TextParser.parseMedia().
// See http://b/168253400
if (mediaState.waitingToClearBuffer) {
shaka.log.info(logPrefix, 'waitingToClearBuffer, skip append');
mediaState.performingUpdate = false;
this.scheduleUpdate_(mediaState, 0);
return;
}
await this.append_(
mediaState, presentationTime, stream, reference, result);
}
if (mediaState.segmentPrefetch && mediaState.segmentIterator) {
mediaState.segmentPrefetch.prefetchSegmentsByTime(
reference.startTime, /* skipFirst= */ true);
}
} else {
if (this.config_.lowLatencyMode && !isReadableStreamSupported) {
shaka.log.warning('Low latency streaming mode is enabled, but ' +
'ReadableStream is not supported by the browser.');
}
const fetchSegment = this.fetch_(mediaState, reference);
const result = await fetchSegment;
this.destroyer_.ensureNotDestroyed();
if (this.fatalError_) {
return;
}
this.destroyer_.ensureNotDestroyed();
// If the text stream gets switched between fetch_() and append_(), the
// new text parser is initialized, but the new init segment is not
// fetched yet. That would cause an error in TextParser.parseMedia().
// See http://b/168253400
if (mediaState.waitingToClearBuffer) {
shaka.log.info(logPrefix, 'waitingToClearBuffer, skip append');
mediaState.performingUpdate = false;
this.scheduleUpdate_(mediaState, 0);
return;
}
await this.append_(
mediaState, presentationTime, stream, reference, result);
}
this.destroyer_.ensureNotDestroyed();
if (this.fatalError_) {
return;
}
// move to next segment after appending the current segment.
mediaState.lastSegmentReference = reference;
const newRef = iter.next().value;
shaka.log.v2(logPrefix, 'advancing to next segment', newRef);
mediaState.performingUpdate = false;
mediaState.recovering = false;
const info = this.playerInterface_.mediaSourceEngine.getBufferedInfo();
const buffered = info[mediaState.type];
// Convert the buffered object to a string capture its properties on
// WebOS.
shaka.log.v1(logPrefix, 'finished fetch and append',
JSON.stringify(buffered));
if (!mediaState.waitingToClearBuffer) {
this.playerInterface_.onSegmentAppended(reference, mediaState.stream);
}
// Update right away.
this.scheduleUpdate_(mediaState, 0);
} catch (error) {
this.destroyer_.ensureNotDestroyed(error);
if (this.fatalError_) {
return;
}
goog.asserts.assert(error instanceof shaka.util.Error,
'Should only receive a Shaka error');
mediaState.performingUpdate = false;
if (error.code == shaka.util.Error.Code.OPERATION_ABORTED) {
// If the network slows down, abort the current fetch request and start
// a new one, and ignore the error message.
mediaState.performingUpdate = false;
this.cancelUpdate_(mediaState);
this.scheduleUpdate_(mediaState, 0);
} else if (mediaState.type == ContentType.TEXT &&
this.config_.ignoreTextStreamFailures) {
if (error.code == shaka.util.Error.Code.BAD_HTTP_STATUS) {
shaka.log.warning(logPrefix,
'Text stream failed to download. Proceeding without it.');
} else {
shaka.log.warning(logPrefix,
'Text stream failed to parse. Proceeding without it.');
}
this.mediaStates_.delete(ContentType.TEXT);
} else if (error.code == shaka.util.Error.Code.QUOTA_EXCEEDED_ERROR) {
this.handleQuotaExceeded_(mediaState, error);
} else {
shaka.log.error(logPrefix, 'failed fetch and append: code=' +
error.code);
mediaState.hasError = true;
if (error.category == shaka.util.Error.Category.NETWORK &&
mediaState.segmentPrefetch) {
mediaState.segmentPrefetch.removeReference(reference);
}
error.severity = shaka.util.Error.Severity.CRITICAL;
await this.handleStreamingError_(mediaState, error);
}
}
}
/**
* @param {!BufferSource} rawResult
* @param {shaka.extern.aesKey} aesKey
* @param {number} position
* @return {!Promise.<!BufferSource>} finalResult
* @private
*/
async aesDecrypt_(rawResult, aesKey, position) {
const key = aesKey;
if (!key.cryptoKey) {
goog.asserts.assert(key.fetchKey, 'If AES cryptoKey was not ' +
'preloaded, fetchKey function should be provided');
await key.fetchKey();
goog.asserts.assert(key.cryptoKey, 'AES cryptoKey should now be set');
}
let iv = key.iv;
if (!iv) {
iv = shaka.util.BufferUtils.toUint8(new ArrayBuffer(16));
let sequence = key.firstMediaSequenceNumber + position;
for (let i = iv.byteLength - 1; i >= 0; i--) {
iv[i] = sequence & 0xff;
sequence >>= 8;
}
}
let algorithm;
if (aesKey.blockCipherMode == 'CBC') {
algorithm = {
name: 'AES-CBC',
iv,
};
} else {
algorithm = {
name: 'AES-CTR',
counter: iv,
// NIST SP800-38A standard suggests that the counter should occupy half
// of the counter block
length: 64,
};
}
return window.crypto.subtle.decrypt(algorithm, key.cryptoKey, rawResult);
}
/**
* Clear per-stream error states and retry any failed streams.
* @param {number} delaySeconds
* @return {boolean} False if unable to retry.
*/
retry(delaySeconds) {
if (this.destroyer_.destroyed()) {
shaka.log.error('Unable to retry after StreamingEngine is destroyed!');
return false;
}
if (this.fatalError_) {
shaka.log.error('Unable to retry after StreamingEngine encountered a ' +
'fatal error!');
return false;
}
for (const mediaState of this.mediaStates_.values()) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
// Only schedule an update if it has an error, but it's not mid-update
// and there is not already an update scheduled.
if (mediaState.hasError && !mediaState.performingUpdate &&
!mediaState.updateTimer) {
shaka.log.info(logPrefix, 'Retrying after failure...');
mediaState.hasError = false;
this.scheduleUpdate_(mediaState, delaySeconds);
}
}
return true;
}
/**
* Append the data to the remaining data.
* @param {!Uint8Array} remaining
* @param {!Uint8Array} data
* @return {!Uint8Array}
* @private
*/
concatArray_(remaining, data) {
const result = new Uint8Array(remaining.length + data.length);
result.set(remaining);
result.set(data, remaining.length);
return result;
}
/**
* Handles a QUOTA_EXCEEDED_ERROR.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @param {!shaka.util.Error} error
* @private
*/
handleQuotaExceeded_(mediaState, error) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
// The segment cannot fit into the SourceBuffer. Ideally, MediaSource would
// have evicted old data to accommodate the segment; however, it may have
// failed to do this if the segment is very large, or if it could not find
// a suitable time range to remove.
//
// We can overcome the latter by trying to append the segment again;
// however, to avoid continuous QuotaExceededErrors we must reduce the size
// of the buffer going forward.
//
// If we've recently reduced the buffering goals, wait until the stream
// which caused the first QuotaExceededError recovers. Doing this ensures
// we don't reduce the buffering goals too quickly.
const mediaStates = Array.from(this.mediaStates_.values());
const waitingForAnotherStreamToRecover = mediaStates.some((ms) => {
return ms != mediaState && ms.recovering;
});
if (!waitingForAnotherStreamToRecover) {
if (this.config_.maxDisabledTime > 0) {
const handled = this.playerInterface_.disableStream(
mediaState.stream, this.config_.maxDisabledTime);
if (handled) {
return;
}
}
// Reduction schedule: 80%, 60%, 40%, 20%, 16%, 12%, 8%, 4%, fail.
// Note: percentages are used for comparisons to avoid rounding errors.
const percentBefore = Math.round(100 * this.bufferingGoalScale_);
if (percentBefore > 20) {
this.bufferingGoalScale_ -= 0.2;
} else if (percentBefore > 4) {
this.bufferingGoalScale_ -= 0.04;
} else {
shaka.log.error(
logPrefix, 'MediaSource threw QuotaExceededError too many times');
mediaState.hasError = true;
this.fatalError_ = true;
this.playerInterface_.onError(error);
return;
}
const percentAfter = Math.round(100 * this.bufferingGoalScale_);
shaka.log.warning(
logPrefix,
'MediaSource threw QuotaExceededError:',
'reducing buffering goals by ' + (100 - percentAfter) + '%');
mediaState.recovering = true;
} else {
shaka.log.debug(
logPrefix,
'MediaSource threw QuotaExceededError:',
'waiting for another stream to recover...');
}
// QuotaExceededError gets thrown if eviction didn't help to make room
// for a segment. We want to wait for a while (4 seconds is just an
// arbitrary number) before updating to give the playhead a chance to
// advance, so we don't immediately throw again.
this.scheduleUpdate_(mediaState, 4);
}
/**
* Sets the given MediaState's associated SourceBuffer's timestamp offset,
* append window, and init segment if they have changed. If an error occurs
* then neither the timestamp offset or init segment are unset, since another
* call to switch() will end up superseding them.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @param {!shaka.media.SegmentReference} reference
* @return {!Promise}
* @private
*/
async initSourceBuffer_(mediaState, reference) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const MimeUtils = shaka.util.MimeUtils;
const StreamingEngine = shaka.media.StreamingEngine;
const logPrefix = StreamingEngine.logPrefix_(mediaState);
/** @type {!Array.<!Promise>} */
const operations = [];
// Rounding issues can cause us to remove the first frame of a Period, so
// reduce the window start time slightly.
const appendWindowStart = Math.max(0,
Math.max(reference.appendWindowStart, this.playRangeStart_) -
StreamingEngine.APPEND_WINDOW_START_FUDGE_);
const appendWindowEnd =
Math.min(reference.appendWindowEnd, this.playRangeEnd_) +
StreamingEngine.APPEND_WINDOW_END_FUDGE_;
goog.asserts.assert(
reference.startTime <= appendWindowEnd,
logPrefix + ' segment should start before append window end');
const codecs = MimeUtils.getCodecBase(mediaState.stream.codecs);
const mimeType = MimeUtils.getBasicType(mediaState.stream.mimeType);
const timestampOffset = reference.timestampOffset;
if (timestampOffset != mediaState.lastTimestampOffset ||
appendWindowStart != mediaState.lastAppendWindowStart ||
appendWindowEnd != mediaState.lastAppendWindowEnd ||
codecs != mediaState.lastCodecs ||
mimeType != mediaState.lastMimeType) {
shaka.log.v1(logPrefix, 'setting timestamp offset to ' + timestampOffset);
shaka.log.v1(logPrefix,
'setting append window start to ' + appendWindowStart);
shaka.log.v1(logPrefix,
'setting append window end to ' + appendWindowEnd);
const isResetMediaSourceNecessary =
mediaState.lastCodecs && mediaState.lastMimeType &&
this.playerInterface_.mediaSourceEngine.isResetMediaSourceNecessary(
mediaState.type, mediaState.stream, mimeType, codecs);
if (isResetMediaSourceNecessary) {
let otherState = null;
if (mediaState.type === ContentType.VIDEO) {
otherState = this.mediaStates_.get(ContentType.AUDIO);
} else if (mediaState.type === ContentType.AUDIO) {
otherState = this.mediaStates_.get(ContentType.VIDEO);
}
if (otherState) {
// First, abort all operations in progress on the other stream.
await this.abortOperations_(otherState).catch(() => {});
// Then clear our cache of the last init segment, since MSE will be
// reloaded and no init segment will be there post-reload.
otherState.lastInitSegmentReference = null;
// Now force the existing buffer to be cleared. It is not necessary
// to perform the MSE clear operation, but this has the side-effect
// that our state for that stream will then match MSE's post-reload
// state.
this.forceClearBuffer_(otherState);
}
}
const setProperties = async () => {
/**
* @type {!Map.<shaka.util.ManifestParserUtils.ContentType,
* shaka.extern.Stream>}
*/
const streamsByType = new Map();
if (this.currentVariant_.audio) {
streamsByType.set(ContentType.AUDIO, this.currentVariant_.audio);
}
if (this.currentVariant_.video) {
streamsByType.set(ContentType.VIDEO, this.currentVariant_.video);
}
try {
mediaState.lastAppendWindowStart = appendWindowStart;
mediaState.lastAppendWindowEnd = appendWindowEnd;
mediaState.lastCodecs = codecs;
mediaState.lastMimeType = mimeType;
mediaState.lastTimestampOffset = timestampOffset;
const ignoreTimestampOffset = this.manifest_.sequenceMode ||
this.manifest_.type == shaka.media.ManifestParser.HLS;
await this.playerInterface_.mediaSourceEngine.setStreamProperties(
mediaState.type, timestampOffset, appendWindowStart,
appendWindowEnd, ignoreTimestampOffset,
reference.mimeType || mediaState.stream.mimeType,
reference.codecs || mediaState.stream.codecs, streamsByType);
} catch (error) {
mediaState.lastAppendWindowStart = null;
mediaState.lastAppendWindowEnd = null;
mediaState.lastCodecs = null;
mediaState.lastTimestampOffset = null;
throw error;
}
};
// Dispatching init asynchronously causes the sourceBuffers in
// the MediaSourceEngine to become detached do to race conditions
// with mediaSource and sourceBuffers being created simultaneously.
await setProperties();
}
if (!shaka.media.InitSegmentReference.equal(
reference.initSegmentReference, mediaState.lastInitSegmentReference)) {
mediaState.lastInitSegmentReference = reference.initSegmentReference;
if (reference.isIndependent() && reference.initSegmentReference) {
shaka.log.v1(logPrefix, 'fetching init segment');
const fetchInit =
this.fetch_(mediaState, reference.initSegmentReference);
const append = async () => {
try {
const initSegment = await fetchInit;
this.destroyer_.ensureNotDestroyed();
let lastTimescale = null;
const timescaleMap = new Map();
/** @type {!shaka.extern.SpatialVideoInfo} */
const spatialVideoInfo = {
projection: null,
hfov: null,
};
const parser = new shaka.util.Mp4Parser();
const Mp4Parser = shaka.util.Mp4Parser;
const Mp4BoxParsers = shaka.util.Mp4BoxParsers;
parser.box('moov', Mp4Parser.children)
.box('trak', Mp4Parser.children)
.box('mdia', Mp4Parser.children)
.fullBox('mdhd', (box) => {
goog.asserts.assert(
box.version != null,
'MDHD is a full box and should have a valid version.');
const parsedMDHDBox = Mp4BoxParsers.parseMDHD(
box.reader, box.version);
lastTimescale = parsedMDHDBox.timescale;
})
.box('hdlr', (box) => {
const parsedHDLR = Mp4BoxParsers.parseHDLR(box.reader);
switch (parsedHDLR.handlerType) {
case 'soun':
timescaleMap.set(ContentType.AUDIO, lastTimescale);
break;
case 'vide':
timescaleMap.set(ContentType.VIDEO, lastTimescale);
break;
}
lastTimescale = null;
})
.box('minf', Mp4Parser.children)
.box('stbl', Mp4Parser.children)
.fullBox('stsd', Mp4Parser.sampleDescription)
.box('encv', Mp4Parser.visualSampleEntry)
.box('avc1', Mp4Parser.visualSampleEntry)
.box('avc3', Mp4Parser.visualSampleEntry)
.box('hev1', Mp4Parser.visualSampleEntry)
.box('hvc1', Mp4Parser.visualSampleEntry)
.box('dvav', Mp4Parser.visualSampleEntry)
.box('dva1', Mp4Parser.visualSampleEntry)
.box('dvh1', Mp4Parser.visualSampleEntry)
.box('dvhe', Mp4Parser.visualSampleEntry)
.box('vexu', Mp4Parser.children)
.box('proj', Mp4Parser.children)
.fullBox('prji', (box) => {
const parsedPRJIBox = Mp4BoxParsers.parsePRJI(box.reader);
spatialVideoInfo.projection = parsedPRJIBox.projection;
})
.box('hfov', (box) => {
const parsedHFOVBox = Mp4BoxParsers.parseHFOV(box.reader);
spatialVideoInfo.hfov = parsedHFOVBox.hfov;
})
.parse(initSegment);
this.updateSpatialVideoInfo_(spatialVideoInfo);
if (timescaleMap.has(mediaState.type)) {
reference.initSegmentReference.timescale =
timescaleMap.get(mediaState.type);
} else if (lastTimescale != null) {
// Fallback for segments without HDLR box
reference.initSegmentReference.timescale = lastTimescale;
}
shaka.log.v1(logPrefix, 'appending init segment');
const hasClosedCaptions = mediaState.stream.closedCaptions &&
mediaState.stream.closedCaptions.size > 0;
await this.playerInterface_.beforeAppendSegment(
mediaState.type, initSegment);
await this.playerInterface_.mediaSourceEngine.appendBuffer(
mediaState.type, initSegment, /* reference= */ null,
mediaState.stream, hasClosedCaptions);
} catch (error) {
mediaState.lastInitSegmentReference = null;
throw error;
}
};
this.playerInterface_.onInitSegmentAppended(
reference.startTime, reference.initSegmentReference);
operations.push(append());
}
}
if (this.manifest_.sequenceMode) {
const lastDiscontinuitySequence =
mediaState.lastSegmentReference ?
mediaState.lastSegmentReference.discontinuitySequence : null;
// Across discontinuity bounds, we should resync timestamps for
// sequence mode playbacks. The next segment appended should
// land at its theoretical timestamp from the segment index.
if (reference.discontinuitySequence != lastDiscontinuitySequence) {
operations.push(this.playerInterface_.mediaSourceEngine.resync(
mediaState.type, reference.startTime));
}
}
await Promise.all(operations);
}
/**
* Appends the given segment and evicts content if required to append.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @param {number} presentationTime
* @param {shaka.extern.Stream} stream
* @param {!shaka.media.SegmentReference} reference
* @param {BufferSource} segment
* @param {boolean=} isChunkedData
* @return {!Promise}
* @private
*/
async append_(mediaState, presentationTime, stream, reference, segment,
isChunkedData = false) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
const hasClosedCaptions = stream.closedCaptions &&
stream.closedCaptions.size > 0;
let parser;
const hasEmsg = ((stream.emsgSchemeIdUris != null &&
stream.emsgSchemeIdUris.length > 0) ||
this.config_.dispatchAllEmsgBoxes);
const shouldParsePrftBox =
(this.config_.parsePrftBox && !this.parsedPrftEventRaised_);
if (hasEmsg || shouldParsePrftBox) {
parser = new shaka.util.Mp4Parser();
}
if (hasEmsg) {
parser
.fullBox(
'emsg',
(box) => this.parseEMSG_(
reference, stream.emsgSchemeIdUris, box));
}
if (shouldParsePrftBox) {
parser
.fullBox(
'prft',
(box) => this.parsePrft_(
reference, box));
}
if (hasEmsg || shouldParsePrftBox) {
parser.parse(segment);
}
await this.evict_(mediaState, presentationTime);
this.destroyer_.ensureNotDestroyed();
// 'seeked' or 'adaptation' triggered logic applies only to this
// appendBuffer() call.
const seeked = mediaState.seeked;
mediaState.seeked = false;
const adaptation = mediaState.adaptation;
mediaState.adaptation = false;
await this.playerInterface_.beforeAppendSegment(mediaState.type, segment);
await this.playerInterface_.mediaSourceEngine.appendBuffer(
mediaState.type,
segment,
reference,
stream,
hasClosedCaptions,
seeked,
adaptation,
isChunkedData);
this.destroyer_.ensureNotDestroyed();
shaka.log.v2(logPrefix, 'appended media segment');
}
/**
* Parse the EMSG box from a MP4 container.
*
* @param {!shaka.media.SegmentReference} reference
* @param {?Array.<string>} emsgSchemeIdUris Array of emsg
* scheme_id_uri for which emsg boxes should be parsed.
* @param {!shaka.extern.ParsedBox} box
* @private
* https://dashif-documents.azurewebsites.net/Events/master/event.html#emsg-format
* aligned(8) class DASHEventMessageBox
* extends FullBox(‘emsg’, version, flags = 0){
* if (version==0) {
* string scheme_id_uri;
* string value;
* unsigned int(32) timescale;
* unsigned int(32) presentation_time_delta;
* unsigned int(32) event_duration;
* unsigned int(32) id;
* } else if (version==1) {
* unsigned int(32) timescale;
* unsigned int(64) presentation_time;
* unsigned int(32) event_duration;
* unsigned int(32) id;
* string scheme_id_uri;
* string value;
* }
* unsigned int(8) message_data[];
*/
parseEMSG_(reference, emsgSchemeIdUris, box) {
let timescale;
let id;
let eventDuration;
let schemeId;
let startTime;
let presentationTimeDelta;
let value;
if (box.version === 0) {
schemeId = box.reader.readTerminatedString();
value = box.reader.readTerminatedString();
timescale = box.reader.readUint32();
presentationTimeDelta = box.reader.readUint32();
eventDuration = box.reader.readUint32();
id = box.reader.readUint32();
startTime = reference.startTime + (presentationTimeDelta / timescale);
} else {
timescale = box.reader.readUint32();
const pts = box.reader.readUint64();
startTime = (pts / timescale) + reference.timestampOffset;
presentationTimeDelta = startTime - reference.startTime;
eventDuration = box.reader.readUint32();
id = box.reader.readUint32();
schemeId = box.reader.readTerminatedString();
value = box.reader.readTerminatedString();
}
const messageData = box.reader.readBytes(
box.reader.getLength() - box.reader.getPosition());
// See DASH sec. 5.10.3.3.1
// If a DASH client detects an event message box with a scheme that is not
// defined in MPD, the client is expected to ignore it.
if ((emsgSchemeIdUris && emsgSchemeIdUris.includes(schemeId)) ||
this.config_.dispatchAllEmsgBoxes) {
// See DASH sec. 5.10.4.1
// A special scheme in DASH used to signal manifest updates.
if (schemeId == 'urn:mpeg:dash:event:2012') {
this.playerInterface_.onManifestUpdate();
} else {
// All other schemes are dispatched as a general 'emsg' event.
/** @type {shaka.extern.EmsgInfo} */
const emsg = {
startTime: startTime,
endTime: startTime + (eventDuration / timescale),
schemeIdUri: schemeId,
value: value,
timescale: timescale,
presentationTimeDelta: presentationTimeDelta,
eventDuration: eventDuration,
id: id,
messageData: messageData,
};
// Dispatch an event to notify the application about the emsg box.
const eventName = shaka.util.FakeEvent.EventName.Emsg;
const data = (new Map()).set('detail', emsg);
const event = new shaka.util.FakeEvent(eventName, data);
// A user can call preventDefault() on a cancelable event.
event.cancelable = true;
this.playerInterface_.onEvent(event);
if (event.defaultPrevented) {
// If the caller uses preventDefault() on the 'emsg' event, don't
// process any further, and don't generate an ID3 'metadata' event
// for the same data.
return;
}
// Additionally, ID3 events generate a 'metadata' event. This is a
// pre-parsed version of the metadata blob already dispatched in the
// 'emsg' event.
if (schemeId == 'https://aomedia.org/emsg/ID3' ||
schemeId == 'https://developer.apple.com/streaming/emsg-id3') {
// See https://aomediacodec.github.io/id3-emsg/
const frames = shaka.util.Id3Utils.getID3Frames(messageData);
if (frames.length && reference) {
/** @private {shaka.extern.ID3Metadata} */
const metadata = {
cueTime: reference.startTime,
data: messageData,
frames: frames,
dts: reference.startTime,
pts: reference.startTime,
};
this.playerInterface_.onMetadata(
[metadata], /* offset= */ 0, reference.endTime);
}
}
}
}
}
/**
* Parse PRFT box.
* @param {!shaka.media.SegmentReference} reference
* @param {!shaka.extern.ParsedBox} box
* @private
*/
parsePrft_(reference, box) {
if (this.parsedPrftEventRaised_ ||
!reference.initSegmentReference.timescale) {
return;
}
goog.asserts.assert(
box.version == 0 || box.version == 1,
'PRFT version can only be 0 or 1');
const parsed = shaka.util.Mp4BoxParsers.parsePRFTInaccurate(
box.reader, box.version);
const timescale = reference.initSegmentReference.timescale;
const wallClockTime = this.convertNtp(parsed.ntpTimestamp);
const programStartDate = new Date(wallClockTime -
(parsed.mediaTime / timescale) * 1000);
const prftInfo = {
wallClockTime,
programStartDate,
};
const eventName = shaka.util.FakeEvent.EventName.Prft;
const data = (new Map()).set('detail', prftInfo);
const event = new shaka.util.FakeEvent(
eventName, data);
this.playerInterface_.onEvent(event);
this.parsedPrftEventRaised_ = true;
}
/**
* Convert Ntp ntpTimeStamp to UTC Time
*
* @param {number} ntpTimeStamp
* @return {number} utcTime
*/
convertNtp(ntpTimeStamp) {
const start = new Date(Date.UTC(1900, 0, 1, 0, 0, 0));
return new Date(start.getTime() + ntpTimeStamp).getTime();
}
/**
* Evicts media to meet the max buffer behind limit.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @param {number} presentationTime
* @private
*/
async evict_(mediaState, presentationTime) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
shaka.log.v2(logPrefix, 'checking buffer length');
// Use the max segment duration, if it is longer than the bufferBehind, to
// avoid accidentally clearing too much data when dealing with a manifest
// with a long keyframe interval.
const bufferBehind = Math.max(this.config_.bufferBehind,
this.manifest_.presentationTimeline.getMaxSegmentDuration());
const startTime =
this.playerInterface_.mediaSourceEngine.bufferStart(mediaState.type);
if (startTime == null) {
shaka.log.v2(logPrefix,
'buffer behind okay because nothing buffered:',
'presentationTime=' + presentationTime,
'bufferBehind=' + bufferBehind);
return;
}
const bufferedBehind = presentationTime - startTime;
const overflow = bufferedBehind - bufferBehind;
// See: https://github.com/shaka-project/shaka-player/issues/6240
if (overflow <= this.config_.evictionGoal) {
shaka.log.v2(logPrefix,
'buffer behind okay:',
'presentationTime=' + presentationTime,
'bufferedBehind=' + bufferedBehind,
'bufferBehind=' + bufferBehind,
'evictionGoal=' + this.config_.evictionGoal,
'underflow=' + Math.abs(overflow));
return;
}
shaka.log.v1(logPrefix,
'buffer behind too large:',
'presentationTime=' + presentationTime,
'bufferedBehind=' + bufferedBehind,
'bufferBehind=' + bufferBehind,
'evictionGoal=' + this.config_.evictionGoal,
'overflow=' + overflow);
await this.playerInterface_.mediaSourceEngine.remove(mediaState.type,
startTime, startTime + overflow);
this.destroyer_.ensureNotDestroyed();
shaka.log.v1(logPrefix, 'evicted ' + overflow + ' seconds');
}
/**
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @return {boolean}
* @private
*/
static isEmbeddedText_(mediaState) {
const MimeUtils = shaka.util.MimeUtils;
const CEA608_MIME = MimeUtils.CEA608_CLOSED_CAPTION_MIMETYPE;
const CEA708_MIME = MimeUtils.CEA708_CLOSED_CAPTION_MIMETYPE;
return mediaState &&
mediaState.type == shaka.util.ManifestParserUtils.ContentType.TEXT &&
(mediaState.stream.mimeType == CEA608_MIME ||
mediaState.stream.mimeType == CEA708_MIME);
}
/**
* Fetches the given segment.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @param {(!shaka.media.InitSegmentReference|!shaka.media.SegmentReference)}
* reference
* @param {?function(BufferSource):!Promise=} streamDataCallback
*
* @return {!Promise.<BufferSource>}
* @private
*/
async fetch_(mediaState, reference, streamDataCallback) {
const segmentData = reference.getSegmentData();
if (segmentData) {
return segmentData;
}
let op = null;
if (mediaState.segmentPrefetch) {
op = mediaState.segmentPrefetch.getPrefetchedSegment(
reference, streamDataCallback);
}
if (!op) {
op = this.dispatchFetch_(
reference, mediaState.stream, streamDataCallback);
}
let position = 0;
if (mediaState.segmentIterator) {
position = mediaState.segmentIterator.currentPosition();
}
mediaState.operation = op;
const response = await op.promise;
mediaState.operation = null;
let result = response.data;
if (reference.aesKey) {
result = await this.aesDecrypt_(result, reference.aesKey, position);
}
return result;
}
/**
* Fetches the given segment.
*
* @param {!shaka.extern.Stream} stream
* @param {(!shaka.media.InitSegmentReference|!shaka.media.SegmentReference)}
* reference
* @param {?function(BufferSource):!Promise=} streamDataCallback
*
* @return {!shaka.net.NetworkingEngine.PendingRequest}
* @private
*/
dispatchFetch_(reference, stream, streamDataCallback) {
goog.asserts.assert(
this.playerInterface_.netEngine, 'Must have net engine');
return shaka.media.StreamingEngine.dispatchFetch(
reference, stream, streamDataCallback || null,
this.config_.retryParameters, this.playerInterface_.netEngine);
}
/**
* Fetches the given segment.
*
* @param {!shaka.extern.Stream} stream
* @param {(!shaka.media.InitSegmentReference|!shaka.media.SegmentReference)}
* reference
* @param {?function(BufferSource):!Promise} streamDataCallback
* @param {shaka.extern.RetryParameters} retryParameters
* @param {!shaka.net.NetworkingEngine} netEngine
*
* @return {!shaka.net.NetworkingEngine.PendingRequest}
*/
static dispatchFetch(
reference, stream, streamDataCallback, retryParameters, netEngine) {
const requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
const segment = reference instanceof shaka.media.SegmentReference ?
reference : undefined;
const type = segment ?
shaka.net.NetworkingEngine.AdvancedRequestType.MEDIA_SEGMENT :
shaka.net.NetworkingEngine.AdvancedRequestType.INIT_SEGMENT;
const request = shaka.util.Networking.createSegmentRequest(
reference.getUris(),
reference.startByte,
reference.endByte,
retryParameters,
streamDataCallback);
request.contentType = stream.type;
shaka.log.v2('fetching: reference=', reference);
return netEngine.request(requestType, request, {type, stream, segment});
}
/**
* Clears the buffer and schedules another update.
* The optional parameter safeMargin allows to retain a certain amount
* of buffer, which can help avoiding rebuffering events.
* The value of the safe margin should be provided by the ABR manager.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @param {boolean} flush
* @param {number} safeMargin
* @private
*/
async clearBuffer_(mediaState, flush, safeMargin) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
goog.asserts.assert(
!mediaState.performingUpdate && (mediaState.updateTimer == null),
logPrefix + ' unexpected call to clearBuffer_()');
mediaState.waitingToClearBuffer = false;
mediaState.waitingToFlushBuffer = false;
mediaState.clearBufferSafeMargin = 0;
mediaState.clearingBuffer = true;
mediaState.lastSegmentReference = null;
mediaState.segmentIterator = null;
shaka.log.debug(logPrefix, 'clearing buffer');
if (mediaState.segmentPrefetch &&
!this.audioPrefetchMap_.has(mediaState.stream)) {
mediaState.segmentPrefetch.clearAll();
}
if (safeMargin) {
const presentationTime = this.playerInterface_.getPresentationTime();
const duration = this.playerInterface_.mediaSourceEngine.getDuration();
await this.playerInterface_.mediaSourceEngine.remove(
mediaState.type, presentationTime + safeMargin, duration);
} else {
await this.playerInterface_.mediaSourceEngine.clear(mediaState.type);
this.destroyer_.ensureNotDestroyed();
if (flush) {
await this.playerInterface_.mediaSourceEngine.flush(
mediaState.type);
}
}
this.destroyer_.ensureNotDestroyed();
shaka.log.debug(logPrefix, 'cleared buffer');
mediaState.clearingBuffer = false;
mediaState.endOfStream = false;
// Since the clear operation was async, check to make sure we're not doing
// another update and we don't have one scheduled yet.
if (!mediaState.performingUpdate && !mediaState.updateTimer) {
this.scheduleUpdate_(mediaState, 0);
}
}
/**
* Schedules |mediaState|'s next update.
*
* @param {!shaka.media.StreamingEngine.MediaState_} mediaState
* @param {number} delay The delay in seconds.
* @private
*/
scheduleUpdate_(mediaState, delay) {
const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
// If the text's update is canceled and its mediaState is deleted, stop
// scheduling another update.
const type = mediaState.type;
if (type == shaka.util.ManifestParserUtils.ContentType.TEXT &&
!this.mediaStates_.has(type)) {
shaka.log.v1(logPrefix, 'Text stream is unloaded. No update is needed.');
return;
}
shaka.log.v2(logPrefix, 'updating in ' + delay + ' seconds');
goog.asserts.assert(mediaState.updateTimer == null,
logPrefix + ' did not expect update to be scheduled');
mediaState.updateTimer = new shaka.util.DelayedTick(async () => {
try {
await this.onUpdate_(mediaState);
} catch (error) {
if (this.playerInterface_) {
this.playerInterface_.onError(error);
}
}
}).tickAfter(delay);
}
/**
* If |mediaState| is scheduled to update, stop it.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @private
*/
cancelUpdate_(mediaState) {
if (mediaState.updateTimer == null) {
return;
}
mediaState.updateTimer.stop();
mediaState.updateTimer = null;
}
/**
* If |mediaState| holds any in-progress operations, abort them.
*
* @return {!Promise}
* @private
*/
async abortOperations_(mediaState) {
if (mediaState.operation) {
await mediaState.operation.abort();
}
}
/**
* Handle streaming errors by delaying, then notifying the application by
* error callback and by streaming failure callback.
*
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @param {!shaka.util.Error} error
* @return {!Promise}
* @private
*/
async handleStreamingError_(mediaState, error) {
// If we invoke the callback right away, the application could trigger a
// rapid retry cycle that could be very unkind to the server. Instead,
// use the backoff system to delay and backoff the error handling.
await this.failureCallbackBackoff_.attempt();
this.destroyer_.ensureNotDestroyed();
const maxDisabledTime = this.getDisabledTime_(error);
// Try to recover from network errors
if (error.category === shaka.util.Error.Category.NETWORK &&
maxDisabledTime > 0) {
error.handled = this.playerInterface_.disableStream(
mediaState.stream, maxDisabledTime);
// Decrease the error severity to recoverable
if (error.handled) {
error.severity = shaka.util.Error.Severity.RECOVERABLE;
}
}
// First fire an error event.
if (!error.handled ||
error.code != shaka.util.Error.Code.SEGMENT_MISSING) {
this.playerInterface_.onError(error);
}
// If the error was not handled by the application, call the failure
// callback.
if (!error.handled) {
this.config_.failureCallback(error);
}
}
/**
* @param {!shaka.util.Error} error
* @private
*/
getDisabledTime_(error) {
if (this.config_.maxDisabledTime === 0 &&
error.code == shaka.util.Error.Code.SEGMENT_MISSING) {
// Spec: https://datatracker.ietf.org/doc/html/draft-pantos-hls-rfc8216bis#section-6.3.3
// The client SHOULD NOT attempt to load Media Segments that have been
// marked with an EXT-X-GAP tag, or to load Partial Segments with a
// GAP=YES attribute. Instead, clients are encouraged to look for
// another Variant Stream of the same Rendition which does not have the
// same gap, and play that instead.
return 1;
}
return this.config_.maxDisabledTime;
}
/**
* Reset Media Source
*
* @return {!Promise.<boolean>}
*/
async resetMediaSource() {
const now = (Date.now() / 1000);
const minTimeBetweenRecoveries = this.config_.minTimeBetweenRecoveries;
if (!this.config_.allowMediaSourceRecoveries ||
(now - this.lastMediaSourceReset_) < minTimeBetweenRecoveries) {
return false;
}
this.lastMediaSourceReset_ = now;
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const audioMediaState = this.mediaStates_.get(ContentType.AUDIO);
if (audioMediaState) {
audioMediaState.lastInitSegmentReference = null;
this.forceClearBuffer_(audioMediaState);
this.abortOperations_(audioMediaState).catch(() => {});
}
const videoMediaState = this.mediaStates_.get(ContentType.VIDEO);
if (videoMediaState) {
videoMediaState.lastInitSegmentReference = null;
this.forceClearBuffer_(videoMediaState);
this.abortOperations_(videoMediaState).catch(() => {});
}
/**
* @type {!Map.<shaka.util.ManifestParserUtils.ContentType,
* shaka.extern.Stream>}
*/
const streamsByType = new Map();
if (this.currentVariant_.audio) {
streamsByType.set(ContentType.AUDIO, this.currentVariant_.audio);
}
if (this.currentVariant_.video) {
streamsByType.set(ContentType.VIDEO, this.currentVariant_.video);
}
await this.playerInterface_.mediaSourceEngine.reset(streamsByType);
return true;
}
/**
* Update the spatial video info and notify to the app.
*
* @param {shaka.extern.SpatialVideoInfo} info
* @private
*/
updateSpatialVideoInfo_(info) {
if (this.spatialVideoInfo_.projection != info.projection ||
this.spatialVideoInfo_.hfov != info.hfov) {
const EventName = shaka.util.FakeEvent.EventName;
let event;
if (info.projection != null || info.hfov != null) {
const eventName = EventName.SpatialVideoInfoEvent;
const data = (new Map()).set('detail', info);
event = new shaka.util.FakeEvent(eventName, data);
} else {
const eventName = EventName.NoSpatialVideoInfoEvent;
event = new shaka.util.FakeEvent(eventName);
}
event.cancelable = true;
this.playerInterface_.onEvent(event);
this.spatialVideoInfo_ = info;
}
}
/**
* Update the segment iterator direction.
*
* @private
*/
updateSegmentIteratorReverse_() {
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const reverse = this.playerInterface_.getPlaybackRate() < 0;
const videoState = this.mediaStates_.get(ContentType.VIDEO);
if (videoState && videoState.segmentIterator) {
videoState.segmentIterator.setReverse(reverse);
}
const audioState = this.mediaStates_.get(ContentType.AUDIO);
if (audioState && audioState.segmentIterator) {
audioState.segmentIterator.setReverse(reverse);
}
const textState = this.mediaStates_.get(ContentType.TEXT);
if (textState && textState.segmentIterator) {
textState.segmentIterator.setReverse(reverse);
}
}
/**
* @param {shaka.media.StreamingEngine.MediaState_} mediaState
* @return {string} A log prefix of the form ($CONTENT_TYPE:$STREAM_ID), e.g.,
* "(audio:5)" or "(video:hd)".
* @private
*/
static logPrefix_(mediaState) {
return '(' + mediaState.type + ':' + mediaState.stream.id + ')';
}
};
/**
* @typedef {{
* getPresentationTime: function():number,
* getBandwidthEstimate: function():number,
* getPlaybackRate: function():number,
* mediaSourceEngine: !shaka.media.MediaSourceEngine,
* netEngine: shaka.net.NetworkingEngine,
* onError: function(!shaka.util.Error),
* onEvent: function(!Event),
* onManifestUpdate: function(),
* onSegmentAppended: function(!shaka.media.SegmentReference,
* !shaka.extern.Stream),
* onInitSegmentAppended: function(!number,!shaka.media.InitSegmentReference),
* beforeAppendSegment: function(
* shaka.util.ManifestParserUtils.ContentType,!BufferSource):Promise,
* onMetadata: !function(!Array.<shaka.extern.ID3Metadata>, number, ?number),
* disableStream: function(!shaka.extern.Stream, number):boolean
* }}
*
* @property {function():number} getPresentationTime
* Get the position in the presentation (in seconds) of the content that the
* viewer is seeing on screen right now.
* @property {function():number} getBandwidthEstimate
* Get the estimated bandwidth in bits per second.
* @property {function():number} getPlaybackRate
* Get the playback rate
* @property {!shaka.media.MediaSourceEngine} mediaSourceEngine
* The MediaSourceEngine. The caller retains ownership.
* @property {shaka.net.NetworkingEngine} netEngine
* The NetworkingEngine instance to use. The caller retains ownership.
* @property {function(!shaka.util.Error)} onError
* Called when an error occurs. If the error is recoverable (see
* {@link shaka.util.Error}) then the caller may invoke either
* StreamingEngine.switch*() or StreamingEngine.seeked() to attempt recovery.
* @property {function(!Event)} onEvent
* Called when an event occurs that should be sent to the app.
* @property {function()} onManifestUpdate
* Called when an embedded 'emsg' box should trigger a manifest update.
* @property {function(!shaka.media.SegmentReference,
* !shaka.extern.Stream)} onSegmentAppended
* Called after a segment is successfully appended to a MediaSource.
* @property
* {function(!number, !shaka.media.InitSegmentReference)} onInitSegmentAppended
* Called when an init segment is appended to a MediaSource.
* @property {!function(shaka.util.ManifestParserUtils.ContentType,
* !BufferSource):Promise} beforeAppendSegment
* A function called just before appending to the source buffer.
* @property
* {!function(!Array.<shaka.extern.ID3Metadata>, number, ?number)} onMetadata
* Called when an ID3 is found in a EMSG.
* @property {function(!shaka.extern.Stream, number):boolean} disableStream
* Called to temporarily disable a stream i.e. disabling all variant
* containing said stream.
*/
shaka.media.StreamingEngine.PlayerInterface;
/**
* @typedef {{
* type: shaka.util.ManifestParserUtils.ContentType,
* stream: shaka.extern.Stream,
* segmentIterator: shaka.media.SegmentIterator,
* lastSegmentReference: shaka.media.SegmentReference,
* lastInitSegmentReference: shaka.media.InitSegmentReference,
* lastTimestampOffset: ?number,
* lastAppendWindowStart: ?number,
* lastAppendWindowEnd: ?number,
* lastCodecs: ?string,
* lastMimeType: ?string,
* restoreStreamAfterTrickPlay: ?shaka.extern.Stream,
* endOfStream: boolean,
* performingUpdate: boolean,
* updateTimer: shaka.util.DelayedTick,
* waitingToClearBuffer: boolean,
* waitingToFlushBuffer: boolean,
* clearBufferSafeMargin: number,
* clearingBuffer: boolean,
* seeked: boolean,
* adaptation: boolean,
* recovering: boolean,
* hasError: boolean,
* operation: shaka.net.NetworkingEngine.PendingRequest,
* segmentPrefetch: shaka.media.SegmentPrefetch
* }}
*
* @description
* Contains the state of a logical stream, i.e., a sequence of segmented data
* for a particular content type. At any given time there is a Stream object
* associated with the state of the logical stream.
*
* @property {shaka.util.ManifestParserUtils.ContentType} type
* The stream's content type, e.g., 'audio', 'video', or 'text'.
* @property {shaka.extern.Stream} stream
* The current Stream.
* @property {shaka.media.SegmentIndexIterator} segmentIterator
* An iterator through the segments of |stream|.
* @property {shaka.media.SegmentReference} lastSegmentReference
* The SegmentReference of the last segment that was appended.
* @property {shaka.media.InitSegmentReference} lastInitSegmentReference
* The InitSegmentReference of the last init segment that was appended.
* @property {?number} lastTimestampOffset
* The last timestamp offset given to MediaSourceEngine for this type.
* @property {?number} lastAppendWindowStart
* The last append window start given to MediaSourceEngine for this type.
* @property {?number} lastAppendWindowEnd
* The last append window end given to MediaSourceEngine for this type.
* @property {?string} lastCodecs
* The last append codecs given to MediaSourceEngine for this type.
* @property {?string} lastMimeType
* The last append mime type given to MediaSourceEngine for this type.
* @property {?shaka.extern.Stream} restoreStreamAfterTrickPlay
* The Stream to restore after trick play mode is turned off.
* @property {boolean} endOfStream
* True indicates that the end of the buffer has hit the end of the
* presentation.
* @property {boolean} performingUpdate
* True indicates that an update is in progress.
* @property {shaka.util.DelayedTick} updateTimer
* A timer used to update the media state.
* @property {boolean} waitingToClearBuffer
* True indicates that the buffer must be cleared after the current update
* finishes.
* @property {boolean} waitingToFlushBuffer
* True indicates that the buffer must be flushed after it is cleared.
* @property {number} clearBufferSafeMargin
* The amount of buffer to retain when clearing the buffer after the update.
* @property {boolean} clearingBuffer
* True indicates that the buffer is being cleared.
* @property {boolean} seeked
* True indicates that the presentation just seeked.
* @property {boolean} adaptation
* True indicates that the presentation just automatically switched variants.
* @property {boolean} recovering
* True indicates that the last segment was not appended because it could not
* fit in the buffer.
* @property {boolean} hasError
* True indicates that the stream has encountered an error and has stopped
* updating.
* @property {shaka.net.NetworkingEngine.PendingRequest} operation
* Operation with the number of bytes to be downloaded.
* @property {?shaka.media.SegmentPrefetch} segmentPrefetch
* A prefetch object for managing prefetching. Null if unneeded
* (if prefetching is disabled, etc).
*/
shaka.media.StreamingEngine.MediaState_;
/**
* The fudge factor for appendWindowStart. By adjusting the window backward, we
* avoid rounding errors that could cause us to remove the keyframe at the start
* of the Period.
*
* NOTE: This was increased as part of the solution to
* https://github.com/shaka-project/shaka-player/issues/1281
*
* @const {number}
* @private
*/
shaka.media.StreamingEngine.APPEND_WINDOW_START_FUDGE_ = 0.1;
/**
* The fudge factor for appendWindowEnd. By adjusting the window backward, we
* avoid rounding errors that could cause us to remove the last few samples of
* the Period. This rounding error could then create an artificial gap and a
* stutter when the gap-jumping logic takes over.
*
* https://github.com/shaka-project/shaka-player/issues/1597
*
* @const {number}
* @private
*/
shaka.media.StreamingEngine.APPEND_WINDOW_END_FUDGE_ = 0.01;
/**
* The maximum number of segments by which a stream can get ahead of other
* streams.
*
* Introduced to keep StreamingEngine from letting one media type get too far
* ahead of another. For example, audio segments are typically much smaller
* than video segments, so in the time it takes to fetch one video segment, we
* could fetch many audio segments. This doesn't help with buffering, though,
* since the intersection of the two buffered ranges is what counts.
*
* @const {number}
* @private
*/
shaka.media.StreamingEngine.MAX_RUN_AHEAD_SEGMENTS_ = 1;