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Unexpected ffmpeg conversion results

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Ralph Stevenson
Unexpected ffmpeg conversion results
on Feb 8, 2012 at 7:13:04 pm

Hi all. I'm using ffmpeg to reduce video captured by my Hauppauge HD PVR from 59.94fps to 29.97fps. My first experiment produced exactly the result I was expecting:

ffmpeg -i in.mp4 -sameq -r 29.97 out.mp4

in: 15.4mb out: 8.4mb (total bit rate: 1112)

Then I go to do this again:
ffmpeg -i in2.mp4 -sameq -r 29.97 out2.mp4

Unexpected result:
in: 15.9mb out: 18.0mb (total bit rate: 2383)

Now, the two input files ARE different video files, but I'd still expect consistent results:

in.mp4: 60s, 15.4mb, 59.94fps, 640x480, h.264, aac, total bit rate: 2039
in2.mp4: 60s, 15.9mb, 59.94fps, 640x480, h.264, aac, total bit rate: 2105

Using -qscale produces similarly odd results. Any ideas what could be causing this?


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