videojs-contrib-media-sources/src/transmuxer_worker.js

A Media Source Extensions plugin for video.js

/**
 * videojs-contrib-media-sources
 *
 * Copyright (c) 2015 Brightcove
 * All rights reserved.
 *
 * Handles communication between the browser-world and the mux.js
 * transmuxer running inside of a WebWorker by exposing a simple
 * message-based interface to a Transmuxer object.
 */
var
  muxjs = {},
  transmuxer,
  initOptions = {};

importScripts('../node_modules/mux.js/lib/utils/stream.js');
importScripts('../node_modules/mux.js/lib/utils/exp-golomb.js');
importScripts('../node_modules/mux.js/lib/mp4/mp4-generator.js');
importScripts('../node_modules/mux.js/lib/codecs/aac.js');
importScripts('../node_modules/mux.js/lib/codecs/h264.js');
importScripts('../node_modules/mux.js/lib/m2ts/m2ts.js');
importScripts('../node_modules/mux.js/lib/m2ts/caption-stream.js');
importScripts('../node_modules/mux.js/lib/m2ts/metadata-stream.js');
importScripts('../node_modules/mux.js/lib/mp4/transmuxer.js');

/**
 * wireTransmuxerEvents
 * Re-emits tranmsuxer events by converting them into messages to the
 * world outside the worker
 */
var wireTransmuxerEvents = function (transmuxer) {
  transmuxer.on('data', function (segment) {
    // transfer ownership of the underlying ArrayBuffer instead of doing a copy to save memory
    // ArrayBuffers are transferable but generic TypedArrays are not
    // see https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers#Passing_data_by_transferring_ownership_(transferable_objects)
    segment.data = segment.data.buffer;
    postMessage({
      action: 'data',
      segment: segment
    }, [segment.data]);
  });

  if (transmuxer.captionStream) {
    transmuxer.captionStream.on('data', function(caption) {
      postMessage({
        action: 'caption',
        data: caption
      });
    });
  }

  transmuxer.on('done', function (data) {
    postMessage({ action: 'done' });
  });
};

/**
 * All incoming messages route through this hash. If no function exists
 * to handle an incoming message, then we ignore the message.
 */
var messageHandlers = {
  /**
   * init
   * Allows you to initialize the transmuxer and pass along options from
   * outside the worker
   */
  init: function (data) {
    initOptions = (data && data.options) || {};
    this.defaultInit();
  },
  /**
   * defaultInit
   * Is called before every function and initializes the transmuxer with
   * default options if `init` was never explicitly called
   */
  defaultInit: function () {
    if (transmuxer) {
      transmuxer.dispose();
    }
    transmuxer = new muxjs.mp4.Transmuxer(initOptions);
    wireTransmuxerEvents(transmuxer);
  },
  /**
   * push
   * Adds data (a ts segment) to the start of the transmuxer pipeline for
   * processing
   */
  push: function (data) {
    // Cast array buffer to correct type for transmuxer
    var segment = new Uint8Array(data.data);
    transmuxer.push(segment);
  },
  /**
   * reset
   * Recreate the transmuxer so that the next segment added via `push`
   * start with a fresh transmuxer
   */
  reset: function () {
    this.defaultInit();
  },
  /**
   * setTimestampOffset
   * Set the value that will be used as the `baseMediaDecodeTime` time for the
   * next segment pushed in. Subsequent segments will have their `baseMediaDecodeTime`
   * set relative to the first based on the PTS values.
   */
  setTimestampOffset: function (data) {
    var timestampOffset = data.timestampOffset || 0;
    transmuxer.setBaseMediaDecodeTime(Math.round(timestampOffset * 90000));
  },
  /**
   * flush
   * Forces the pipeline to finish processing the last segment and emit it's
   * results
   */
  flush: function (data) {
    transmuxer.flush();
  }
};

onmessage = function(event) {
  // Setup the default transmuxer if one doesn't exist yet and we are invoked with
  // an action other than `init`
  if (!transmuxer && event.data.action !== 'init') {
    messageHandlers.defaultInit();
  }

  if (event.data && event.data.action) {
    if (messageHandlers[event.data.action]) {
      messageHandlers[event.data.action](event.data);
    }
  }
};