av/cmd/mjpeg-player/player.js

/*
AUTHOR
  Trek Hopton <trek@ausocean.org>

LICENSE
  This file is Copyright (C) 2020 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License in gpl.txt.
  If not, see http://www.gnu.org/licenses.
*/

let frameRate = 25; //Keeps track of the frame rate, default is 25fps.
self.importScripts('./lex-mjpeg.js');
self.importScripts('./hlsjs/mts-demuxer.js');

const codecs = {
  MJPEG: 1,
  MTS_MJPEG: 2,
}

// onmessage is called whenever the main thread sends this worker a message.
onmessage = e => {
  switch (e.data.msg) {
    case "setFrameRate":
      frameRate = e.data.data;
      break;
    case "loadMjpeg":
      player = new PlayerWorker();
      player.init(codecs.MJPEG);
      player.append(e.data.data);
      player.setFrameRate(frameRate);
      player.start();
      break;
    case "loadMtsMjpeg":
      player = new PlayerWorker();
      player.init(codecs.MTS_MJPEG);
      player.append(e.data.data);
      player.start();
      break;
    case "appendMtsMjpeg":
      player.append(e.data.data);
      break;
    default:
      console.error("unknown message from main thread");
      break;
  }
};

// PlayerWorker has a FrameBuffer to hold frames and once started, passes them one at a time to the main thread.
class PlayerWorker {
  init(codec) {
    this.frameRate = frameRate;
    this.codec = codec;
    switch (codec) {
      case codecs.MJPEG:
        this.frameSrc = new MJPEGLexer();
        break;
      case codecs.MTS_MJPEG:
        this.frameSrc = new FrameBuffer();
        break;
    }
  }

  setFrameRate(rate) {
    this.frameRate = rate;
  }

  start() {
    let frame = this.frameSrc.read();
    if (frame != null) {
      postMessage({ msg: "frame", data: frame.buffer }, [frame.buffer]);
      setTimeout(() => { this.start(); }, 1000 / this.frameRate);
    } else {
      postMessage({ msg: "stop" });
    }
  }

  append(data) {
    this.frameSrc.append(data);
  }
}

// FrameBuffer allows an array of subarrays (MJPEG frames) to be read one at a time.
class FrameBuffer {
  constructor() {
    this.segments = [];
    this.off = { segment: 0, frame: 0 };
    this.demuxer = new MTSDemuxer();
  }

  // read returns the next single frame.
  read() {
    let off = this.off;
    let prevOff = off;
    if (this.incrementOff()) {
      return this.segments[prevOff.segment][prevOff.frame];
    } else {
      return null;
    }
  }

  append(data) {
    let demuxed = this.demuxer.demux(new Uint8Array(data));
    this.segments.push(demuxed.data);
  }

  incrementOff() {
    if (!this.segments || !this.segments[this.off.segment]) {
      return false;
    }
    if (this.off.frame + 1 >= this.segments[this.off.segment].length) {
      if (this.off.segment + 1 >= this.segments.length) {
        return false;
      } else {
        this.off.segment++;
        this.off.frame = 0;
        return true;
      }
    } else {
      this.off.frame++;
      return true;
    }
  }
}