recently I've been messing around with FFMPEG and streams through Nodejs. My ultimate goal is to serve a transcoded video stream - from any input filetype - via HTTP, generated in real-time as it's needed in segments.
I'm currently attempting to handle this using HLS. I pre-generate a dummy m3u8 manifest using the known duration of the input video. It contains a bunch of URLs that point to individual constant-duration segments. Then, once the client player starts requesting the individual URLs, I use the requested path to determine which time range of video the client needs. Then I transcode the video and stream that segment back to them.
Now for the problem: This approach mostly works, but has a small audio bug. Currently, with most test input files, my code produces a video that - while playable - seems to have a very small (< .25 second) audio skip at the start of each segment.
I think this may be an issue with splitting using time in ffmpeg, where possibly the audio stream cannot be accurately sliced at the exact frame the video is. So far, I've been unable to figure out a solution to this problem.
If anybody has any direction they can steer me - or even a prexisting library/server that solves this use-case - I appreciate the guidance. My knowledge of video encoding is fairly limited.
I'll include an example of my relevant current code below, so others can see where I'm stuck. You should be able to run this as a Nodejs Express server, then point any HLS player at localhost:8080/master to load the manifest and begin playback. See the transcode.get('/segment/:seg.ts' line at the end, for the relevant transcoding bit.
'use strict';
const express = require('express');
const ffmpeg = require('fluent-ffmpeg');
let PORT = 8080;
let HOST = 'localhost';
const transcode = express();
/*
* This file demonstrates an Express-based server, which transcodes & streams a video file.
* All transcoding is handled in memory, in chunks, as needed by the player.
*
* It works by generating a fake manifest file for an HLS stream, at the endpoint "/m3u8".
* This manifest contains links to each "segment" video clip, which browser-side HLS players will load as-needed.
*
* The "/segment/:seg.ts" endpoint is the request destination for each clip,
* and uses FFMpeg to generate each segment on-the-fly, based off which segment is requested.
*/
const pathToMovie = 'C:\\input-file.mp4'; // The input file to stream as HLS.
const segmentDur = 5; // Controls the duration (in seconds) that the file will be chopped into.
const getMetadata = async(file) => {
return new Promise( resolve => {
ffmpeg.ffprobe(file, function(err, metadata) {
console.log(metadata);
resolve(metadata);
});
});
};
// Generate a "master" m3u8 file, which the player should point to:
transcode.get('/master', async(req, res) => {
res.set({"Content-Disposition":"attachment; filename=\"m3u8.m3u8\""});
res.send(`#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=150000
/m3u8?num=1
#EXT-X-STREAM-INF:BANDWIDTH=240000
/m3u8?num=2`)
});
// Generate an m3u8 file to emulate a premade video manifest. Guesses segments based off duration.
transcode.get('/m3u8', async(req, res) => {
let met = await getMetadata(pathToMovie);
let duration = met.format.duration;
let out = '#EXTM3U\n' +
'#EXT-X-VERSION:3\n' +
`#EXT-X-TARGETDURATION:${segmentDur}\n` +
'#EXT-X-MEDIA-SEQUENCE:0\n' +
'#EXT-X-PLAYLIST-TYPE:VOD\n';
let splits = Math.max(duration / segmentDur);
for(let i=0; i< splits; i++){
out += `#EXTINF:${segmentDur},\n/segment/${i}.ts\n`;
}
out+='#EXT-X-ENDLIST\n';
res.set({"Content-Disposition":"attachment; filename=\"m3u8.m3u8\""});
res.send(out);
});
// Transcode the input video file into segments, using the given segment number as time offset:
transcode.get('/segment/:seg.ts', async(req, res) => {
const segment = req.params.seg;
const time = segment * segmentDur;
let proc = new ffmpeg({source: pathToMovie})
.seekInput(time)
.duration(segmentDur)
.outputOptions('-preset faster')
.outputOptions('-g 50')
.outputOptions('-profile:v main')
.withAudioCodec('aac')
.outputOptions('-ar 48000')
.withAudioBitrate('155k')
.withVideoBitrate('1000k')
.outputOptions('-c:v h264')
.outputOptions(`-output_ts_offset ${time}`)
.format('mpegts')
.on('error', function(err, st, ste) {
console.log('an error happened:', err, st, ste);
}).on('progress', function(progress) {
console.log(progress);
})
.pipe(res, {end: true});
});
transcode.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`);
