@sqhead/mux.js/lib/rawH264/coalesce-stream.js

A collection of lightweight utilities for inspecting and manipulating video container formats.

'use strict';

var Stream = require('../utils/stream.js');
var mp4 = require('../mp4/mp4-generator.js');


var VIDEO_PROPERTIES = [
  'width',
  'height',
  'profileIdc',
  'levelIdc',
  'profileCompatibility'
];


/**
 * A Stream that can combine multiple streams (ie. audio & video)
 * into a single output segment for MSE. Also supports audio-only
 * and video-only streams.
 */
var CoalesceStream = function(options) {
  // Number of Tracks per output segment
  // If greater than 1, we combine multiple
  // tracks into a single segment
  this.numberOfTracks = 0;

  this.pendingTracks = [];
  this.pendingBoxes = [];
  this.videoTrack = null;
  this.pendingBytes = 0;
  this.emittedTracks = 0;

  CoalesceStream.prototype.init.call(this);

  // Take output from multiple
  this.push = function(output) {
    // Add this track to the list of pending tracks and store
    // important information required for the construction of
    // the final segment
    this.pendingTracks.push(output.track);
    this.pendingBoxes.push(output.boxes);
    this.pendingBytes += output.boxes.byteLength;

    if (output.track.type === 'video') {
      this.videoTrack = output.track;
    } else {
        console.log("Error: unknown output type: " + output.track.type);
    }
  };
};

CoalesceStream.prototype = new Stream();
CoalesceStream.prototype.flush = function(flushSource) {
  var
    offset = 0,
    event = {
      captions: [],
      captionStreams: {},
      metadata: [],
      info: {}
    },
    initSegment,
    i;

  if (this.pendingTracks.length < this.numberOfTracks) {
    if (flushSource !== 'VideoSegmentStream') {
      // Return because we haven't received a flush from a data-generating
      // portion of the segment (meaning that we have only recieved meta-data
      // or captions.)
      return;
    } else if (this.pendingTracks.length === 0) {
      // In the case where we receive a flush without any data having been
      // received we consider it an emitted track for the purposes of coalescing
      // `done` events.
      // We do this for the case where there is an audio and video track in the
      // segment but no audio data. (seen in several playlists with alternate
      // audio tracks and no audio present in the main TS segments.)
      this.emittedTracks++;

      if (this.emittedTracks >= this.numberOfTracks) {
        this.trigger('done');
        this.emittedTracks = 0;
      }
      return;
    }
  }

  if (this.videoTrack) {
    VIDEO_PROPERTIES.forEach(function(prop) {
      event.info[prop] = this.videoTrack[prop];
    }, this);
  }

  if (this.pendingTracks.length === 1) {
    event.type = this.pendingTracks[0].type;
  } else {
    event.type = 'combined';
  }

  this.emittedTracks += this.pendingTracks.length;

  initSegment = mp4.initSegment(this.pendingTracks);

  // Create a new typed array to hold the init segment
  event.initSegment = new Uint8Array(initSegment.byteLength);

  // Create an init segment containing a moov
  // and track definitions
  event.initSegment.set(initSegment);

  // Create a new typed array to hold the moof+mdats
  event.data = new Uint8Array(this.pendingBytes);

  // Append each moof+mdat (one per track) together
  for (i = 0; i < this.pendingBoxes.length; i++) {
    event.data.set(this.pendingBoxes[i], offset);
    offset += this.pendingBoxes[i].byteLength;
  }

  // Reset stream state
  this.pendingTracks.length = 0;
  this.videoTrack = null;
  this.pendingBoxes.length = 0;
  this.pendingBytes = 0;

  // Emit the built segment
  this.trigger('data', event);

  // Only emit `done` if all tracks have been flushed and emitted
  if (this.emittedTracks >= this.numberOfTracks) {
    this.trigger('done');
    this.emittedTracks = 0;
  }
};

module.exports = CoalesceStream;