Moritz,
On Fri Oct 16 13:51:11 EEST 2020, FFmpeg user discussions wrote:
On Fri, Oct 16, 2020 at 20:26:16 +1100, FFmpeg user discussions wrote:
People,
I truncated a 14s file with:
ffmpeg -i 20201016_055828.mp4 -t 00:00:09 -async 1 cut.mp4
and although about 35% of the frames were removed, the resulting mp4
was double the size - why is this? I did a before and after mediainfo
comparison - see here:
http://pricom.com.au/Diff.html
and the only things that jump out at me are:
Format settings : CABAC / 4 Ref Frames
Format settings, Reference frames : 4 frame
ie changed from 1 to 4 . . but is that the explanation?
I am using:
ffmpeg-4.2.4-1.fc31.x86_64
Thanks,
Phil.
You are reencoding the streams inside the file. ffmpeg's default
encoding parameters apparently result in streams with more bandwidth.
You can fine-tune the encoding parameters, of course.
Re-encoding is not a good idea, as it always loses quality. If you just
want to "clip", be sure to use the "copy" codec:
$ ffmpeg -i 20201016_055828.mp4 -t 00:00:09 -c copy cut.mp4
(Note that cutting without re-encoding may or may not be exact. Feel
free to test first though.)
Ah! . . of course . .
Thanks!
Phil.
--
Philip Rhoades
PO Box 896
Cowra NSW 2794
Australia
E-mail: p...@pricom.com.au
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