There are two ffmpeg commands. First one is used to seek and copy video chunk. Second one is used to transcode video chunk applying select filter for exact frames match.
Here is how:
ffmpeg -ss <sec_from> -to <sec_to> -copyts -i <input> -map 0:v:0 -c copy chunk.mp4ffmpeg -copyts -i chunk.mp4 -vf 'select=between(pts\,<pts_from>\,<pts_to>)' transcoded_cunk.mp4
It works fine most of the times. But for some inputs there is a little pts drift in downloaded chunk so missing frames is possible. In other words pts of the same packets (compared by hash) are shifted by several points (in my case 0,0002 sec) between input and chunked output.
What is the possible reason for such pts drift?
UPDATE 1: That's because ffmpeg set timescale=1000 in mvhd atom so edit list media time to start from looses precision. Is it possible to force mvhd timescale?
UPDATE 2: It's not possible to change mvhd timescale because ffmpeg uses constant (MOV_TIMESCALE 1000):
UPDATE 3: same issue discussed earlier
