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Subtitles from pipe or fifo?

Discussions about problems encountered using ffmpeg.
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Subtitles from pipe or fifo?

Postby lbdroidman » Fri Jun 30, 2017 8:12 pm

I'm using ffmpeg to capture video from several v4l2 cameras into an mkv container. I would also like to add in a subtitle or other data track that is generated from a live NMEA data stream (GPS logs).

I tried to modify gpspipe (part of gpsd) to output the data in SubRip format (srt) and feed it to a fifo. I was successful in that the modified gpspipe produces a correct srt output, but silly ffmpeg wants to see the end of the file before it will start working with it. This obviously won't happen until gpspipe closes the fifo.

I am aware of how I could achieve gps log subtitles using drawtext with reload, but there are a number of problems with this approach;
1) It will not be possible to extract the subtitles back to text.
2) the hardcoded subtitles will obscure the video.
3) the raspberry pi's CPU isn't powerful enough to do this on a live stream.

And just to add even more complexity to the situation;
1) I'm segmenting the output every 60 seconds,
2) There is the potential for uncontrolled power loss at any moment.
Meaning, of course, that it is non-trivial to add in the subtitles later on.

Anybody have any suggestions as to how one might mux in a live stream of text?
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