transcode video streams using node.js Streams and avconv (aka ffmpeg)

gistfile1.md

The avconv utility can be made to work in 'the Unix way' by specifying stdin and/or stdout instead of filenames for the input and output respectively. See: http://libav.org/avconv.html#pipe

Example:

cat input.ts | avconv -i pipe:0 -f mp4 -movflags frag_keyframe pipe:1 | cat > output.mp4

Using node's require('child_process').spawn(), we can pipe streams of video data through avconv's stdin and stdout and thus Stream All The Things.

var fs = require('fs');
var child = require('child_process');

var input_file = fs.createReadStream('./input.ts');
var output_file = fs.createWriteStream('./output.mp4');

var args = ['-i', 'pipe:0', '-f', 'mp4', '-movflags', 'frag_keyframe', 'pipe:1'];
var trans_proc = child.spawn('avconv', args, null);

input_file.pipe(trans_proc.stdin);
trans_proc.stdout.pipe(output_file);

trans_proc.stderr.on('data', function (data) {
	console.log(data.toString());
});

ok. This should fit nicely in navcodec, I will take a look at it asap.

The biggest problem right now is that the open function in navcodec returns a Media object with some metadata, but using streams this is not easy. So for the stream support I will probably need to have a separate API...

Defining an output as stream is on the other hand quite easy.

Here are a couple random notes:
1.) child_process.spawn() blocks the event loop while the child process is forking. This may not be a big deal here, but see node-spawn-async by @davepacheco for details.

2.) Experimentation has led me to switch from avconv(1) to ffmpeg(1) from ffmpeg.org. For some reason, avconv(1) can't seem to keep up with realtime encoding from mpegts/mpeg-2 to mp4/h.264 when using a udp stream as the source.

Great! I am going to use this in tvheadendWebplayer. Did you try out the current master of avconv?

Thanks for the ffmpeg command. Just what I was looking for. :)