av/cmd/mjpeg-player/player.js

/*
NAME
  player.js

AUTHOR
  Trek Hopton <trek@ausocean.org>

LICENSE
  This file is Copyright (C) 2019 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 [GNU licenses](http://www.gnu.org/licenses).
*/

let frameRate = 30;

onmessage = e => {
    switch(e.data.msg){
        case "setFrameRate":
            frameRate = e.data.data;
            break;
        case "loadMjpeg":
            self.importScripts('./lex-mjpeg.js');
            let mjpeg = new Uint8Array(e.data.data);
            let lex = new MJPEGLexer(mjpeg);
            player = new Player(lex);
            player.setFrameRate(frameRate);
            player.start();
            break;
        case "loadMtsMjpeg":
            self.importScripts('./hlsjs/mts-demuxer.js');
            let mtsMjpeg = new Uint8Array(e.data.data);
            let demux = new MTSDemuxer();
            let tracks = demux._getTracks();
            demux.append(mtsMjpeg);
            buf = new FrameBuffer(tracks.video.data);
            player = new Player(buf);
            player.setFrameRate(frameRate); //TODO: read frame rate from metadata.
            player.start();
            break;
        default:
            console.error("unknown message from main thread");
            break;
    }
};

class Player{
    constructor(buffer){
        this.buffer = buffer;
        this.frameRate = frameRate;
    }

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

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

// FrameBuffer allows an array of subarrays (MJPEG frames) to be read one at a time.
class FrameBuffer{
    constructor(src){
        this.src = src;
        this.off = 0;
    }

    // read returns the next single frame.
    read(){
        return this.src[this.off++];
    }
}