On 2025-08-24 05:20 am, Ulf Zibis wrote:
Hi,
Transcoding of this 3.39 second video
<http://www.jugkoeln.de/Projects/ffmpeg/20241130_000929_01.mp4> took
very long time (speed=0.00316x). Additionally the size of the result
<http://www.jugkoeln.de/Projects/ffmpeg/20241130_000929_01_out.mp4>
was 6 times of the original, even it was scaled by half. And the
result is not playable correctly with VLC media player and ffplay.
...
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '20241130_000929_01.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
creation_time : 2024-11-29T23:09:29.000000Z
com.android.version: 14
Duration: 00:00:03.39, start: 0.000000, bitrate: 54240 kb/s
Stream #0:0[0x1](eng): Video: h264 (High) (avc1 / 0x31637661),
yuv420p(tv, bt709, progressive), 1920x1440, 54638 kb/s, 72 fps, 90k
tbr, 90k tbn (default)
...
frame=302481 fps=284 q=-1.0 Lsize= 133300kB time=00:00:03.36
bitrate=324913.7kbits/s dup=302239 drop=0 speed=0.00316x
The input video is VFR and it apparently has some very short frames so
ffmpeg detects its rate as 90000.
MP4 output defaults to constant frame rate so ffmpeg duplicates frames
to achieve the registered frame rate.
In this case, set an option to keep original frame count as-is.
ffmpeg -i $Video -c:a copy -vf scale=iw/2:ih/2 -fps_mode passthrough
-movflags +faststart Komp/$Video
Regards,
Gyan
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