From the documentation here: https://trac.ffmpeg.org/wiki/Concatenate
If you have MP4 files, these could be losslessly concatenated by first transcoding them to MPEG-2 transport streams. With H.264 video and AAC audio, the following can be used:
ffmpeg -i input1.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
ffmpeg -i input2.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
ffmpeg -i "concat:intermediate1.ts|intermediate2.ts" -c copy -bsf:a aac_adtstoasc output.mp4
This approach works on all platforms.
I needed the ability to encapsulate this in a cross platform script, so I used fluent-ffmpeg and came up with the following solution:
const unlink = path =>
new Promise((resolve, reject) =>
fs.unlink(path, err => (err ? reject(err) : resolve()))
)
const createIntermediate = file =>
new Promise((resolve, reject) => {
const out = `${Math.random()
.toString(13)
.slice(2)}.ts`
ffmpeg(file)
.outputOptions('-c', 'copy', '-bsf:v', 'h264_mp4toannexb', '-f', 'mpegts')
.output(out)
.on('end', () => resolve(out))
.on('error', reject)
.run()
})
const concat = async (files, output) => {
const names = await Promise.all(files.map(createIntermediate))
const namesString = names.join('|')
await new Promise((resolve, reject) =>
ffmpeg(`concat:${namesString}`)
.outputOptions('-c', 'copy', '-bsf:a', 'aac_adtstoasc')
.output(output)
.on('end', resolve)
.on('error', reject)
.run()
)
names.map(unlink)
}
concat(['file1.mp4', 'file2.mp4', 'file3.mp4'], 'output.mp4').then(() =>
console.log('done!')
)