[FFmpeg-user] Crop and transpose filters combined produces large output

Clay D. Montgomery clay at montgomery1.com
Thu Jun 29 18:49:23 EEST 2017


I have been experimenting with using the video crop and transpose 
filters with ffmpeg (version 2.5.2 on Windows) to convert 4K video into 
1080p video without scaling. When I combine these filters in a 1 pass 
operation, I get an output (File4.mp4) that is about 4X larger than it 
should be. But, when I split the same operation into 2 passes, I get an 
output (File3.mp4) that seems to be the correct size. The details are:

Crop and transpose in 1 pass:
     ffmpeg -i File1.mp4 -vf crop=1080:1920:0:0 -vf transpose=2 File4.mp4

File sizes in bytes:
     File1.mp4     79,889,077    (Input 4K Video)
     File4.mp4     25,918,758    (Excessive Size)

Crop and transpose in 2 passes:
     ffmpeg -i File1.mp4 -vf crop=1080:1920:0:0 File2.mp4
     ffmpeg -i File2.mp4 -vf transpose=2 File3.mp4

File sizes in bytes:
     File1.mp4  79,889,077    (Same Input 4K Video)
     File2.mp4    6,994,548
     File3.mp4    5,777,801    (Correct Size)

All of these files can be played with ffplay, but I use other video 
players and they have trouble playing File4.mp4.
It is not a big problem to use 2 passes, but I'm curious if this is a 
known issue or am I missing something?

Thanks, Clay

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