On 02-05-2022 10:18, Paul B Mahol wrote:
On Mon, May 2, 2022 at 9:54 AM Alexander Solonsky <
[email protected]> wrote:
Monday, May 2, 2022, 2:21:17 PM, you wrote:
On Mon, May 2, 2022 at 7:27 AM Alexander Solonsky via ffmpeg-user <
[email protected]> wrote:
Dear Experts,
I'm trying to split an input file into 2 second chunks, transcode and
assemble using a concat muxer. And experiencing two problems:
major one:
1) when using ffmpeg -ss 00:00:08 -t 2 -i <input_file> -c:v libx264 ....
instead of seeking to second 8, ffmpeg seeks somewhere to second 15 or so.
The first segments are correct, and then it start to go haywire.
Using accurate seek ffmpeg -i <input_file> -ss 00:00:08 -t 2 -c:v
libx264 .... resolves the problem. But it is completely unusuble if you
want to split the whole file.
Minor one:
2) when concatenating the resulting files - there happens a noticeable
break between the chunks. For both audio and video and is equal to 2
additional frame durations (e.g. prev chunk ends at 1.981333 and the next
chunk (after concat) while it should start at 2.023000 actually starts at
2.095744 for 24 fps video, and for audio prev chunk ends at 1.927256 and
starts at 2.023220 while it should start at 1.950476).
adding all additional flags like copyts, copytb, enctimebase, vsync
doesn't change anything. And it's really curious when using the hls demuxer
- it splits the file accurately and fast, without these breaks.
Can you please help me fix those two problems or suggest to understand
which command like I could use to reproduce splitting behavior from the HLS
demuxer?
HLS demuxer is a totally different beast than ffmpeg, it operates from
an audio/video stream (from hlssink2) and it generates keyframes when
desired e.g. when the stream needs cutting it generates a keyframe for
that purpose from which the cut can be made.
ffmpeg works with the encoded audio/video container that has fixed
keyframes, if you want the same behaviour you will need to work with
uncompressed audio/video.
greetings
Ferdi Scholten
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