jsmpeg

jsmpeg

An MPEG1 Video Decoder in JavaScript

jsmpeg is a MPEG1 Decoder, written in JavaScript. It's "hand ported", i.e. not compiled with emscripten or similar. This will probably make it obsolete with the advent of asmjs.

Some demos and more info: phoboslab.org/log/2013/05/mpeg1-video-decoder-in-javascript

Usage

// Synopsis: var player = new jsmpeg(urlToFile, options);
// The 'options' argument and all of its properties is optional. If no canvas element 
// is given, jsmpeg will create its own, to be accessed at .canvas

// Example:
var canvas = document.getElementById('videoCanvas');
var player = new jsmpeg('file.mpeg', {canvas: canvas, autoplay: true, loop: true});

player.pause();
player.play();
player.stops();


// An 'onload' callback can be specified in the 'options' argument
var mpegLoaded = function( player ) {
	console.log('Loaded', player);
}
var player = new jsmpeg('file.mpeg', {onload:mpegLoaded});

// If you don't use 'autoplay' and don't explicitly call .play(), you can get individual
// video frames (a canvas element) like so:
var frame = null;
while( (frame = player.nextFrame()) ) {
	someOtherCanvasContext.drawImage(frame, 0, 0);
}

Limitations

• Playback can only start when the file is fully loaded. I'm waiting for chunked XHR with ArrayBuffers to arrive in browsers.
• MPEG files with B-Frames look weird - frames are not reordered. This should be relatively easy to fix, but most encoders seem to not use B-Frames at all by default.
• The width of the MPEG video has to be a multiple of 2.
• Only raw MPEG video streams are supported. The decoder hates Stream Packet Headers in between macroblocks.

You can use FFmpeg to encode videos in a suited format. This will crop the size to a multiple of 2, omit B-Frames and force a raw video stream:

ffmpeg -i in.mp4 -f mpeg1video -vf "crop=iw-mod(iw\,2):ih-mod(ih\,2)" -b 0 out.mpg