shaka-player
Version:
DASH/EME video player library
278 lines (253 loc) • 8.24 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.require('goog.asserts');
goog.require('shaka.net.NetworkingEngine');
goog.require('shaka.media.InitSegmentReference');
goog.require('shaka.media.SegmentReference');
goog.provide('shaka.media.SegmentPrefetch');
goog.require('shaka.log');
/**
* @summary
* This class manages segment prefetch operations.
* Called by StreamingEngine to prefetch next N segments
* ahead of playhead, to reduce the chances of rebuffering.
*/
shaka.media.SegmentPrefetch = class {
/**
* @param {number} prefetchLimit
* @param {shaka.extern.Stream} stream
* @param {shaka.media.SegmentPrefetch.FetchDispatcher} fetchDispatcher
*/
constructor(prefetchLimit, stream, fetchDispatcher) {
/** @private {number} */
this.prefetchLimit_ = prefetchLimit;
/** @private {shaka.extern.Stream} */
this.stream_ = stream;
/** @private {number} */
this.prefetchPosTime_ = 0;
/** @private {shaka.media.SegmentPrefetch.FetchDispatcher} */
this.fetchDispatcher_ = fetchDispatcher;
/**
* @private {!Map.<shaka.media.SegmentReference,
* !shaka.media.SegmentPrefetchOperation>}
*/
this.segmentPrefetchMap_ = new Map();
}
/**
* Fetch next segments ahead of current segment.
*
* @param {(!shaka.media.SegmentReference)} startReference
* @public
*/
prefetchSegments(startReference) {
goog.asserts.assert(this.prefetchLimit_ > 0,
'SegmentPrefetch can not be used when prefetchLimit <= 0.');
const logPrefix = shaka.media.SegmentPrefetch.logPrefix_(this.stream_);
if (!this.stream_.segmentIndex) {
shaka.log.info(logPrefix, 'missing segmentIndex');
return;
}
const currTime = startReference.startTime;
const maxTime = Math.max(currTime, this.prefetchPosTime_);
const iterator = this.stream_.segmentIndex.getIteratorForTime(maxTime);
if (!iterator) {
return;
}
let reference = startReference;
while (this.segmentPrefetchMap_.size < this.prefetchLimit_ &&
reference != null) {
// By default doesn't prefech preload partial segments when using
// byterange
let prefetchAllowed = true;
if (reference.isPreload() && reference.endByte != null) {
prefetchAllowed = false;
}
if (reference.getStatus() ==
shaka.media.SegmentReference.Status.MISSING) {
prefetchAllowed = false;
}
if (prefetchAllowed && !this.segmentPrefetchMap_.has(reference)) {
const segmentPrefetchOperation =
new shaka.media.SegmentPrefetchOperation(this.fetchDispatcher_);
segmentPrefetchOperation.dispatchFetch(reference, this.stream_);
this.segmentPrefetchMap_.set(reference, segmentPrefetchOperation);
}
this.prefetchPosTime_ = reference.startTime;
reference = iterator.next().value;
}
}
/**
* Get the result of prefetched segment if already exists.
* @param {(!shaka.media.SegmentReference)} reference
* @param {?function(BufferSource):!Promise=} streamDataCallback
* @return {?shaka.net.NetworkingEngine.PendingRequest} op
* @public
*/
getPrefetchedSegment(reference, streamDataCallback) {
goog.asserts.assert(this.prefetchLimit_ > 0,
'SegmentPrefetch can not be used when prefetchLimit <= 0.');
goog.asserts.assert(reference instanceof shaka.media.SegmentReference,
'getPrefetchedSegment is only used for shaka.media.SegmentReference.');
const logPrefix = shaka.media.SegmentPrefetch.logPrefix_(this.stream_);
if (this.segmentPrefetchMap_.has(reference)) {
const segmentPrefetchOperation = this.segmentPrefetchMap_.get(reference);
if (streamDataCallback) {
segmentPrefetchOperation.setStreamDataCallback(streamDataCallback);
}
this.segmentPrefetchMap_.delete(reference);
shaka.log.debug(
logPrefix,
'reused prefetched segment at time:', reference.startTime,
'mapSize', this.segmentPrefetchMap_.size);
return segmentPrefetchOperation.getOperation();
} else {
shaka.log.debug(
logPrefix,
'missed segment at time:', reference.startTime,
'mapSize', this.segmentPrefetchMap_.size);
return null;
}
}
/**
* Clear all segment data.
* @public
*/
clearAll() {
if (this.segmentPrefetchMap_.size === 0) {
return;
}
const logPrefix = shaka.media.SegmentPrefetch.logPrefix_(this.stream_);
for (const reference of this.segmentPrefetchMap_.keys()) {
if (reference) {
this.abortPrefetchedSegment_(reference);
}
}
shaka.log.info(logPrefix, 'cleared all');
this.prefetchPosTime_ = 0;
}
/**
* Reset the prefetchLimit and clear all internal states.
* Called by StreamingEngine when configure() was called.
* @param {number} newPrefetchLimit
* @public
*/
resetLimit(newPrefetchLimit) {
goog.asserts.assert(newPrefetchLimit >= 0,
'The new prefetch limit must be >= 0.');
this.prefetchLimit_ = newPrefetchLimit;
const keyArr = Array.from(this.segmentPrefetchMap_.keys());
while (keyArr.length > newPrefetchLimit) {
const reference = keyArr.pop();
if (reference) {
this.abortPrefetchedSegment_(reference);
}
}
}
/**
* Called by Streaming Engine when switching variant.
* @param {shaka.extern.Stream} stream
* @public
*/
switchStream(stream) {
if (stream && stream !== this.stream_) {
this.clearAll();
this.stream_ = stream;
}
}
/**
* Remove a segment from prefetch map and abort it.
* @param {(!shaka.media.SegmentReference)} reference
* @private
*/
abortPrefetchedSegment_(reference) {
const logPrefix = shaka.media.SegmentPrefetch.logPrefix_(this.stream_);
const segmentPrefetchOperation = this.segmentPrefetchMap_.get(reference);
this.segmentPrefetchMap_.delete(reference);
if (segmentPrefetchOperation) {
segmentPrefetchOperation.abort();
shaka.log.info(
logPrefix,
'pop and abort prefetched segment at time:', reference.startTime);
}
}
/**
* The prefix of the logs that are created in this class.
* @return {string}
* @private
*/
static logPrefix_(stream) {
return 'SegmentPrefetch(' + stream.type + ':' + stream.id + ')';
}
};
/**
* @summary
* This class manages a segment prefetch operation.
*/
shaka.media.SegmentPrefetchOperation = class {
/**
* @param {shaka.media.SegmentPrefetch.FetchDispatcher} fetchDispatcher
*/
constructor(fetchDispatcher) {
/** @private {shaka.media.SegmentPrefetch.FetchDispatcher} */
this.fetchDispatcher_ = fetchDispatcher;
/** @private {?function(BufferSource):!Promise} */
this.streamDataCallback_ = null;
/** @private {?shaka.net.NetworkingEngine.PendingRequest} */
this.operation_ = null;
}
/**
* Fetch a segments
*
* @param {!shaka.media.SegmentReference}
* reference
* @param {!shaka.extern.Stream} stream
* @public
*/
dispatchFetch(reference, stream) {
this.operation_ = this.fetchDispatcher_(
reference, stream, async (data) => {
if (this.streamDataCallback_) {
await this.streamDataCallback_(data);
}
});
}
/**
* Get the operation of prefetched segment if already exists.
*
* @return {?shaka.net.NetworkingEngine.PendingRequest} op
* @public
*/
getOperation() {
return this.operation_;
}
/**
* @param {?function(BufferSource):!Promise} streamDataCallback
* @public
*/
setStreamDataCallback(streamDataCallback) {
this.streamDataCallback_ = streamDataCallback;
}
/**
* Abort the current operation if exists.
*/
abort() {
if (this.operation_) {
this.operation_.abort();
}
}
};
/**
* @typedef {function(
* !(shaka.media.InitSegmentReference|shaka.media.SegmentReference),
* shaka.extern.Stream,
* ?function(BufferSource):!Promise=
* ):!shaka.net.NetworkingEngine.PendingRequest}
*
* @description
* A callback function that fetches a segment.
* @export
*/
shaka.media.SegmentPrefetch.FetchDispatcher;