FFMPEG: Transmux mpegts to mp4 gives error: muxer does not support non seekable output

Question

When piping mpegts to ffmpeg, which should convert it to mp4 and pipe to stdout, ffmpeg says: "muxer does not support non seekable output".

After a lot of research I came to the conclusion that mp4 is a bad choice for doing those kinds of on-the-fly transcoding due to seeking. So in essence: MP4 cannot be piped through ffmpeg, which kind of makes sense.

But I do not have a contiguous mpegts stream, I have chunks of 5 seconds. So it's really just like:

• Here is my 1 mb *.ts file
• Please read it from pipe until you hit EOF
• Please transmux it to mp4 (if you really have to seek, well use a buffer)
• Please pipe the complete internal mp4 buffer to stdout

I need these mp4 chunks for a HTML5 MediaSource, the fragmentation is no problem, I use mp4box.js, which works like a charm.

Questions:

• Can FFMPEG do this kind of internal buffering ?
• Is there any better option to consider ?

In essence: Can I (somehow) interact with ffmpeg without using files ? My current solutions works with files and polling for new chunks, which is ugly.

If you are interested in my ffmpeg command, just let me know.

Answer 1

Since you mentioned fragmentation then you can just enable it with movflags. Example for fragments starting on each keyframe:

ffmpeg -i segment.ts -c copy -movflags frag_keyframe+empty_moov -f mp4 -

Having an empty moov atom means it doesn't need to seek and thus works with a pipe.

Answer 2

If you can live with not having a true mp4 format, using ismv actually worked even better for me (didn't damage seeking and total duration info in certain players) than manually adjusting the movflags. According to the ffmpeg formats documentation, the ismv format is similar to mp4, but auto adjusts the movflags for streaming and does a better job of it in my opinion.

Tested in: Firefox, Chrome, VLC

ffmpeg -i input.mp4 -f ismv -

Sadly neither this command nor aergistal's answer create a video compatible for upload to twitter as of 19/12/20 due to twitter's video upload validaiton being very strict and requiring what I imagine is the most common of mp4 formats. So as of right now I still have to use ffmpeg to output directly to a file rather than stdout to allow for twitter video upload. But I would love to hear if anyone has figured out a way around this!