transmuxer-worker.js

/**
 * @file transmuxer-worker.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.
 */
import mp4 from 'mux.js/lib/mp4';

/**
 * Re-emits transmuxer events by converting them into messages to the
 * world outside the worker.
 *
 * @param {Object} transmuxer the transmuxer to wire events on
 * @private
 */
const wireTransmuxerEvents = function(self, 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
    // @link https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers#Passing_data_by_transferring_ownership_(transferable_objects)
    let initArray = segment.initSegment;

    segment.initSegment = {
      data: initArray.buffer,
      byteOffset: initArray.byteOffset,
      byteLength: initArray.byteLength
    };

    let typedArray = segment.data;

    segment.data = typedArray.buffer;
    self.postMessage({
      action: 'data',
      segment,
      byteOffset: typedArray.byteOffset,
      byteLength: typedArray.byteLength
    }, [segment.data]);
  });

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

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

  transmuxer.on('gopInfo', function(gopInfo) {
    self.postMessage({
      action: 'gopInfo',
      gopInfo
    });
  });
};

/**
 * All incoming messages route through this hash. If no function exists
 * to handle an incoming message, then we ignore the message.
 *
 * @class MessageHandlers
 * @param {Object} options the options to initialize with
 */
class MessageHandlers {
  constructor(self, options) {
    this.options = options || {};
    this.self = self;
    this.init();
  }

  /**
   * initialize our web worker and wire all the events.
   */
  init() {
    if (this.transmuxer) {
      this.transmuxer.dispose();
    }
    this.transmuxer = new mp4.Transmuxer(this.options);
    wireTransmuxerEvents(this.self, this.transmuxer);
  }

  /**
   * Adds data (a ts segment) to the start of the transmuxer pipeline for
   * processing.
   *
   * @param {ArrayBuffer} data data to push into the muxer
   */
  push(data) {
    // Cast array buffer to correct type for transmuxer
    let segment = new Uint8Array(data.data, data.byteOffset, data.byteLength);

    this.transmuxer.push(segment);
  }

  /**
   * Recreate the transmuxer so that the next segment added via `push`
   * start with a fresh transmuxer.
   */
  reset() {
    this.init();
  }

  /**
   * 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.
   *
   * @param {Object} data used to set the timestamp offset in the muxer
   */
  setTimestampOffset(data) {
    let timestampOffset = data.timestampOffset || 0;

    this.transmuxer.setBaseMediaDecodeTime(Math.round(timestampOffset * 90000));
  }

  setAudioAppendStart(data) {
    this.transmuxer.setAudioAppendStart(Math.ceil(data.appendStart * 90000));
  }

  /**
   * Forces the pipeline to finish processing the last segment and emit it's
   * results.
   *
   * @param {Object} data event data, not really used
   */
  flush(data) {
    this.transmuxer.flush();
  }

  resetCaptions() {
    this.transmuxer.resetCaptions();
  }

  alignGopsWith(data) {
    this.transmuxer.alignGopsWith(data.gopsToAlignWith.slice());
  }
}

/**
 * Our web wroker interface so that things can talk to mux.js
 * that will be running in a web worker. the scope is passed to this by
 * webworkify.
 *
 * @param {Object} self the scope for the web worker
 */
const TransmuxerWorker = function(self) {
  self.onmessage = function(event) {
    if (event.data.action === 'init' && event.data.options) {
      this.messageHandlers = new MessageHandlers(self, event.data.options);
      return;
    }

    if (!this.messageHandlers) {
      this.messageHandlers = new MessageHandlers(self);
    }

    if (event.data && event.data.action && event.data.action !== 'init') {
      if (this.messageHandlers[event.data.action]) {
        this.messageHandlers[event.data.action](event.data);
      }
    }
  };
};

export default new TransmuxerWorker(self);