116 lines
3.3 KiB
JavaScript
116 lines
3.3 KiB
JavaScript
/**
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* mux.js
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*
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* Copyright (c) Brightcove
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* Licensed Apache-2.0 https://github.com/videojs/mux.js/blob/master/LICENSE
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*
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* Accepts program elementary stream (PES) data events and corrects
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* decode and presentation time stamps to account for a rollover
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* of the 33 bit value.
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*/
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'use strict';
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var Stream = require('../utils/stream');
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var MAX_TS = 8589934592;
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var RO_THRESH = 4294967296;
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var TYPE_SHARED = 'shared';
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var handleRollover = function(value, reference) {
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var direction = 1;
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if (value > reference) {
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// If the current timestamp value is greater than our reference timestamp and we detect a
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// timestamp rollover, this means the roll over is happening in the opposite direction.
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// Example scenario: Enter a long stream/video just after a rollover occurred. The reference
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// point will be set to a small number, e.g. 1. The user then seeks backwards over the
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// rollover point. In loading this segment, the timestamp values will be very large,
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// e.g. 2^33 - 1. Since this comes before the data we loaded previously, we want to adjust
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// the time stamp to be `value - 2^33`.
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direction = -1;
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}
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// Note: A seek forwards or back that is greater than the RO_THRESH (2^32, ~13 hours) will
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// cause an incorrect adjustment.
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while (Math.abs(reference - value) > RO_THRESH) {
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value += (direction * MAX_TS);
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}
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return value;
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};
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var TimestampRolloverStream = function(type) {
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var lastDTS, referenceDTS;
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TimestampRolloverStream.prototype.init.call(this);
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// The "shared" type is used in cases where a stream will contain muxed
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// video and audio. We could use `undefined` here, but having a string
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// makes debugging a little clearer.
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this.type_ = type || TYPE_SHARED;
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this.push = function(data) {
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/**
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* Rollover stream expects data from elementary stream.
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* Elementary stream can push forward 2 types of data
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* - Parsed Video/Audio/Timed-metadata PES (packetized elementary stream) packets
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* - Tracks metadata from PMT (Program Map Table)
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* Rollover stream expects pts/dts info to be available, since it stores lastDTS
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* We should ignore non-PES packets since they may override lastDTS to undefined.
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* lastDTS is important to signal the next segments
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* about rollover from the previous segments.
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*/
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if (data.type === 'metadata') {
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this.trigger('data', data);
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return;
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}
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// Any "shared" rollover streams will accept _all_ data. Otherwise,
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// streams will only accept data that matches their type.
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if (this.type_ !== TYPE_SHARED && data.type !== this.type_) {
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return;
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}
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if (referenceDTS === undefined) {
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referenceDTS = data.dts;
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}
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data.dts = handleRollover(data.dts, referenceDTS);
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data.pts = handleRollover(data.pts, referenceDTS);
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lastDTS = data.dts;
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this.trigger('data', data);
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};
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this.flush = function() {
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referenceDTS = lastDTS;
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this.trigger('done');
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};
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this.endTimeline = function() {
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this.flush();
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this.trigger('endedtimeline');
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};
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this.discontinuity = function() {
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referenceDTS = void 0;
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lastDTS = void 0;
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};
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this.reset = function() {
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this.discontinuity();
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this.trigger('reset');
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};
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};
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TimestampRolloverStream.prototype = new Stream();
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module.exports = {
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TimestampRolloverStream: TimestampRolloverStream,
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handleRollover: handleRollover
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};
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