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Crop, scale and keep quality. Keep getting low bitrates

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Fredric Luthman
Crop, scale and keep quality. Keep getting low bitrates
on May 24, 2013 at 6:03:42 am

Hi,I have several videofiles which are supposed to be presented as 16:9 in a 1280x720 frame. Something has gone wrong in the digitalization and the aspect ratio has gotten wrong. I have figured out that I need to crop and scale. My source-file is h264 and has a video bitrate of about 3000k.

ffmpeg-20130523-git-c54a156-win64-staticbin>ffmpeg -i source.mp4 -acodec copy -vcodec h264 -vf crop=1280:560,scale=1280:720 -qscale 0 -aspect 16:9 source.cropped.mp4

This is the command I use, I though -qscale 0 would work, but the source.cropped-files has a bitrate of about 800k. I realize that I will loose some quality since I crop away 160 vertical pixels (the "black bars").

I guess I can specify a bitrate manually, but is there a better way?

TiA!


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Lou Logan
Re: Crop, scale and keep quality. Keep getting low bitrates
on May 24, 2013 at 11:24:02 pm

libx264 ignores "-qscale". Use "-crf" instead as explained in the FFmpeg and x264 Encoding Guide.

As a semi-related sidenote, as of 2013-04-18, you can use the "-aspect" option with "-vcodec copy" if you only need to change container aspect ratio:
If -aspect is used together with -vcodec copy, it will affect the aspect ratio stored at container level, but not the aspect ratio stored in encoded frames, if it exists.


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