shaka-player
Version:
DASH/EME video player library
315 lines (289 loc) • 9.87 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.util.WebmGenerator');
goog.require('shaka.mkv.BlockFlag');
goog.require('shaka.mkv.ElementId');
goog.require('shaka.mkv.TrackType');
goog.require('shaka.util.BufferUtils');
goog.require('shaka.util.SegmentGenerator');
goog.require('shaka.util.Uint8ArrayUtils');
/**
* Writes the initialization and media segments that MSE plays for WebM: a
* header with one track, and Clusters of SimpleBlocks. It is what Matroska
* needs to become WebM (VP8, Vorbis): WebM is a subset of it, and the frames
* themselves are the same. Blocks that lace several frames are the exception,
* as MSE does not take lacing: each frame gets a block of its own.
*
* @implements {shaka.util.SegmentGenerator}
*/
shaka.util.WebmGenerator = class {
/**
* @param {shaka.util.WebmGenerator.StreamInfo} streamInfo
*/
constructor(streamInfo) {
/** @private {shaka.util.WebmGenerator.StreamInfo} */
this.streamInfo_ = streamInfo;
}
/**
* Generates an initialization segment.
*
* @override
* @return {!Uint8Array}
*/
initSegment() {
const WebmGenerator = shaka.util.WebmGenerator;
const ElementId = shaka.mkv.ElementId;
const header = WebmGenerator.element_(ElementId.EBML,
WebmGenerator.uint_(ElementId.EBML_VERSION, 1),
WebmGenerator.uint_(ElementId.EBML_READ_VERSION, 1),
WebmGenerator.uint_(ElementId.EBML_MAX_ID_LENGTH, 4),
WebmGenerator.uint_(ElementId.EBML_MAX_SIZE_LENGTH, 8),
WebmGenerator.string_(ElementId.DOC_TYPE, 'webm'),
WebmGenerator.uint_(ElementId.DOC_TYPE_VERSION, 4),
WebmGenerator.uint_(ElementId.DOC_TYPE_READ_VERSION, 2));
const info = WebmGenerator.element_(ElementId.INFO,
WebmGenerator.uint_(
ElementId.TIMECODE_SCALE, this.streamInfo_.timecodeScale),
WebmGenerator.string_(ElementId.MUXING_APP, 'Shaka Player'),
WebmGenerator.string_(ElementId.WRITING_APP, 'Shaka Player'));
const tracks = WebmGenerator.element_(
ElementId.TRACKS, this.trackEntry_());
// The Segment has no size, as it goes on for as long as media is appended.
return shaka.util.Uint8ArrayUtils.concat(header,
WebmGenerator.idBytes_(ElementId.SEGMENT),
WebmGenerator.UNKNOWN_SIZE_, info, tracks);
}
/**
* Generates a media segment: one or more Clusters.
*
* @override
* @return {!Uint8Array}
*/
segmentData() {
const WebmGenerator = shaka.util.WebmGenerator;
const ElementId = shaka.mkv.ElementId;
const frames = this.streamInfo_.frames;
const clusters = [];
let start = 0;
while (start < frames.length) {
// A block writes its time as a signed 16-bit number of ticks after the
// time of its Cluster, so a Cluster can only hold so much time.
const clusterTimecode = frames[start].timecode;
let end = start;
const blocks = [];
while (end < frames.length && frames[end].timecode - clusterTimecode <=
WebmGenerator.MAX_CLUSTER_TICKS_) {
blocks.push(this.simpleBlock_(frames[end], clusterTimecode));
end++;
}
clusters.push(WebmGenerator.element_(ElementId.CLUSTER,
WebmGenerator.uint_(ElementId.CLUSTER_TIMECODE, clusterTimecode),
...blocks));
start = end;
}
return shaka.util.Uint8ArrayUtils.concat(...clusters);
}
/**
* @return {!Uint8Array}
* @private
*/
trackEntry_() {
const WebmGenerator = shaka.util.WebmGenerator;
const ElementId = shaka.mkv.ElementId;
const info = this.streamInfo_;
const isVideo = info.type == shaka.mkv.TrackType.VIDEO;
const fields = [
WebmGenerator.uint_(ElementId.TRACK_NUMBER, info.trackNumber),
// The identifier of the track; the number is as unique as anything.
WebmGenerator.uint_(ElementId.TRACK_UID, info.trackNumber),
WebmGenerator.uint_(ElementId.TRACK_TYPE, info.type),
WebmGenerator.string_(ElementId.CODEC_ID, info.codecId),
];
if (info.codecPrivate) {
fields.push(WebmGenerator.element_(
ElementId.CODEC_PRIVATE, info.codecPrivate));
}
if (isVideo) {
fields.push(WebmGenerator.element_(ElementId.VIDEO,
WebmGenerator.uint_(ElementId.PIXEL_WIDTH, info.width),
WebmGenerator.uint_(ElementId.PIXEL_HEIGHT, info.height)));
} else {
fields.push(WebmGenerator.element_(ElementId.AUDIO,
WebmGenerator.float_(ElementId.SAMPLING_FREQUENCY, info.sampleRate),
WebmGenerator.uint_(ElementId.CHANNELS, info.channelCount)));
}
return WebmGenerator.element_(ElementId.TRACK_ENTRY, ...fields);
}
/**
* @param {shaka.util.WebmGenerator.Frame} frame
* @param {number} clusterTimecode
* @return {!Uint8Array}
* @private
*/
simpleBlock_(frame, clusterTimecode) {
const WebmGenerator = shaka.util.WebmGenerator;
const relative = frame.timecode - clusterTimecode;
// The track number is a variable-length integer, whose marker is part of
// its value; a size is the same thing.
const trackNumber = WebmGenerator.sizeVint_(this.streamInfo_.trackNumber);
// The keyframe flag is set on every block of a track that has no other
// kind (audio).
const isKeyframe = frame.keyframe ||
this.streamInfo_.type != shaka.mkv.TrackType.VIDEO;
const flags = isKeyframe ? shaka.mkv.BlockFlag.KEYFRAME : 0;
return WebmGenerator.element_(shaka.mkv.ElementId.SIMPLE_BLOCK,
trackNumber,
new Uint8Array([(relative >> 8) & 0xff, relative & 0xff, flags]),
frame.data);
}
/**
* @param {number} id
* @param {...!Uint8Array} payload
* @return {!Uint8Array}
* @private
*/
static element_(id, ...payload) {
const WebmGenerator = shaka.util.WebmGenerator;
const body = shaka.util.Uint8ArrayUtils.concat(...payload);
return shaka.util.Uint8ArrayUtils.concat(
WebmGenerator.idBytes_(id), WebmGenerator.sizeVint_(body.length), body);
}
/**
* @param {number} id
* @param {number} value
* @return {!Uint8Array}
* @private
*/
static uint_(id, value) {
const bytes = [];
let rest = value;
do {
bytes.unshift(rest % 256);
rest = Math.floor(rest / 256);
} while (rest > 0);
return shaka.util.WebmGenerator.element_(id, new Uint8Array(bytes));
}
/**
* @param {number} id
* @param {number} value
* @return {!Uint8Array}
* @private
*/
static float_(id, value) {
const bytes = new Uint8Array(8);
shaka.util.BufferUtils.toDataView(bytes).setFloat64(0, value);
return shaka.util.WebmGenerator.element_(id, bytes);
}
/**
* @param {number} id
* @param {string} value
* @return {!Uint8Array}
* @private
*/
static string_(id, value) {
return shaka.util.WebmGenerator.element_(id, new Uint8Array(
Array.from(value).map((char) => char.charCodeAt(0))));
}
/**
* @param {number} id An element ID, with its length marker.
* @return {!Uint8Array}
* @private
*/
static idBytes_(id) {
const bytes = [];
for (let rest = id; rest > 0; rest = Math.floor(rest / 256)) {
bytes.unshift(rest % 256);
}
return new Uint8Array(bytes);
}
/**
* Writes a variable-length integer with as few bytes as it can: the number
* of leading zeros of the first byte is the number of bytes that follow it.
*
* @param {number} value
* @return {!Uint8Array}
* @private
*/
static sizeVint_(value) {
for (let length = 1; length <= 8; length++) {
// All the bits set is the reserved "unknown" value.
if (value < Math.pow(2, 7 * length) - 1) {
const bytes = new Uint8Array(length);
let rest = value;
for (let i = length - 1; i >= 0; i--) {
bytes[i] = rest % 256;
rest = Math.floor(rest / 256);
}
bytes[0] |= 0x80 >> (length - 1);
return bytes;
}
}
throw new RangeError('The value does not fit an EBML integer');
}
};
/**
* @typedef {{
* timecode: number,
* data: !Uint8Array,
* keyframe: boolean,
* }}
*
* @property {number} timecode
* The time, in ticks of the timecode scale of the stream.
* @property {!Uint8Array} data
* @property {boolean} keyframe
*/
shaka.util.WebmGenerator.Frame;
/**
* @typedef {{
* trackNumber: number,
* type: number,
* codecId: string,
* codecPrivate: ?Uint8Array,
* timecodeScale: number,
* width: number,
* height: number,
* channelCount: number,
* sampleRate: number,
* frames: !Array<shaka.util.WebmGenerator.Frame>,
* }}
*
* @property {number} trackNumber
* @property {number} type
* A shaka.mkv.TrackType.
* @property {string} codecId
* The Matroska CodecID.
* @property {?Uint8Array} codecPrivate
* @property {number} timecodeScale
* Nanoseconds per tick.
* @property {number} width
* Of a video track.
* @property {number} height
* Of a video track.
* @property {number} channelCount
* Of an audio track.
* @property {number} sampleRate
* Of an audio track.
* @property {!Array<shaka.util.WebmGenerator.Frame>} frames
* The frames of the media segment.
*/
shaka.util.WebmGenerator.StreamInfo;
/**
* The size that EBML writes to say that an element goes on to the end: 8 bytes,
* all the bits of the value set.
*
* @private @const {!Uint8Array}
*/
shaka.util.WebmGenerator.UNKNOWN_SIZE_ =
new Uint8Array([0x01, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]);
/**
* How far apart in time the first and the last block of a Cluster may be. The
* time of a block is a signed 16-bit number of ticks after that of its Cluster,
* so this leaves room for the difference to be rounded.
*
* @private @const {number}
*/
shaka.util.WebmGenerator.MAX_CLUSTER_TICKS_ = 30000;