Hi, how can one change coded_picture_number without fully decoding H.264 frames?
Some context: we have recordings of RTP streams from IP-cameras (fragmented to 10-minutes pieces), made with Janus, and use Janus utility ( https://github.com/meetecho/janus-gateway/blob/master/postprocessing/janus-pp-rec.c, which calls https://github.com/meetecho/janus-gateway/blob/master/postprocessing/pp-h264.c) to convert them to MP4. Resulted MP4 does not play in Google Chrome (though plays in Firefox or VLC); but if "convert" them with: ffmpeg -i janus.mp4 -c copy out.mp4 — then out.mp4 plays well in Chrome. Probable cause of the difference is that in janus.mp4 coded_picture_number starts from non-zero value, and in out.mp4 from zero. I want to patch this utility to enumerate frames from zero. I've managed to do this with parsing AVPacket to AVFrames, but such a way involves full decoding-reencoding and is slow. How can I change coded_picture_number without fully decoding H.264? This is definitely possible, as ffmpeg with `-c copy` does this (and does fast). I've seen ffmpeg source, but don't understand where the key point is. I also found the function av_parser_parse2, which seems to parse without decoding, but it's not clear what to do with its output byte array (all examples use it only for further decoding). Regards, Alexey Golovko.
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