mp4.js

var mp4box = require('mp4box')
var needle = require('needle')
var fs = require('fs')


function iterateCounts(counts, values, fn) {
	var idx = 0;
	counts.forEach(function(count, i) {
		for (var j = 0; j!=count; j++) { fn(values[i], idx++) }
	})
}

function getFramesFromBox(box)
{
	//box.buildSampleLists();
	//var samples = box.moov.traks[0].samples;
	var track = box.moov.traks.filter(function(t) {
		return t.mdia.minf.stbl.stss
	})[0];

	//var stsz = track.mdia.minf.stbl.stsz; // sample table sizes - that's in bytes
	var stts = track.mdia.minf.stbl.stts; // sample table time to sample map
	var ctts = track.mdia.minf.stbl.ctts; // Composition Time Offset  - used to convert DTS to PTS
	var mdhd = track.mdia.mdhd; // media header

	// from stts documentation at https://wiki.multimedia.cx/?title=QuickTime_container#stss
	//    duration = (sample_count1 * sample_time_delta1 + ... + sample_countN * sample_time_deltaN ) / timescale
	var allDts = [ ];
	iterateCounts(stts.sample_counts, stts.sample_deltas, function(delta, idx) { allDts.push(idx * delta) });

	// use ctts to build pts - https://wiki.multimedia.cx/?title=QuickTime_container#ctts
	//console.log(track.mdia.minf.stbl.ctts.sample_counts.length, track.mdia.minf.stbl.ctts.sample_offsets.length, mdhd)
	var allPts = [];
	if (ctts) iterateCounts(ctts.sample_counts, ctts.sample_offsets, function(offset, idx) { allPts.push(allDts[idx] + offset) });

	// we need the stss box - moov.traks[<trackNum>].mdia.minf.stbl.stss - http://wiki.multimedia.cx/?title=QuickTime_container#stss
	// stss - "Sync samples are also known as keyframes or intra-coded frames."
	var frames = track.mdia.minf.stbl.stss.sample_numbers.map(function(x) { 
		// WARNING: in the BBB video, to match ffmpeg we need x+1, in the other, we need x-1; wtf?
		// samples[x].dts/mdhd.timescale
		var dts = allDts[x-1] / mdhd.timescale * 1000;
		var pts = ctts ? allPts[x-1] / mdhd.timescale * 1000 : dts;
		return { dts: dts, pts: pts, timestamp: pts, index: x }
	});

 	// http://bit.ly/1MKue5R - there's a keyframe at the beginning
	if (frames[0] && frames[0].index !== 1) frames.unshift({ timestamp: 0, dts: 0, index: 1 })

	return frames
}

function getForMp4(url, cb) {	
	var box = mp4box.createFile();
	var err, res, pos = 0;
	var maxSeeks = 0;

	function toArrayBuffer(buffer) {
		var ab = new ArrayBuffer(buffer.length);
		var view = new Uint8Array(ab);
		for (var i = 0; i < buffer.length; ++i) view[i] = buffer[i];
		return ab;
	}

	function onData(buf) { 
		var b = toArrayBuffer(buf);
		b.fileStart = pos;
		pos += b.byteLength;
		box.appendBuffer(b);
		if (box.mdats.length && !box.moovStartFound) {
			var offset = box.boxes.map(function(x) { return x.size }).reduce(function(a,b) { return a+b }, 0);
			if (offset > lastOffset) {
				if (maxSeeks > 3) {
					stream.close ? stream.close() : stream.end();
					return cb(new Error('maxSeeks exceeded'));
				}
				maxSeeks++;

				startStream(url, offset);
			}
		}
	}

	var stream, lastOffset = 0;

	function closeStream() {
		if (!stream) return;

		// credit to mafintosh/pump
		if (stream instanceof fs.ReadStream && typeof(stream.close) === 'function') return stream.close() // use close for fs streams to avoid fd leaks
		if (stream.request && typeof(stream.request.abort) === 'function') return stream.request.abort() // request.destroy just do .end - .abort is what we want
		if (typeof(stream.destroy) === 'function') return stream.destroy()
	}

	function startStream(url, offset) {
		//console.log("open stream at "+offset);
		closeStream()

		lastOffset = offset;
		pos = offset;
		if (/^http(s?):\/\//.test(url)) {
			// TODO: WARNING: we should check if the source supports range headers
			// and if the returned range corresponds to the requested range
			// Otherwise, we will eventually end up with a maxSeeks exception (as we would read the beginning of the file over and over, thinking it's actually the next part)
			stream = needle.get(url, { headers: { range: "bytes="+offset+"-" } })
			.on('error', box.onError)
			.on('end', function(e) { box.flush() })
			.on('data', onData)
		} else {
			stream = fs.createReadStream(url, { start: offset })
			.on('error', box.onError)
			.on('end', function() { box.flush() })
			.on('data', onData)
		}
	}

	box.onError = function(err) {
		closeStream()
		cb(err);
	};

	startStream(url, 0);

	box.onReady = function(info) {
		box.flush()
		closeStream()

		if (!info) return cb(new Error("no info returned"));
		if (!info.videoTracks[0]) return cb(new Error("no videoTracks[0]"))

		try {
			var frames = getFramesFromBox(box)
			cb(null, frames)
		} catch(e) { cb(e) }
	}
}


module.exports = getForMp4