[FFmpeg-user] Framerate Question

Jared McIntyre jmcintyre at dfsoftware.com
Tue Mar 6 07:47:20 CET 2012

On Mar 5, 2012, at 3:47 AM, Andrey Utkin wrote:

> I believe x264 encoder is able to compress efficiently in this case,
> without such a hack.

It certainly appears that this scenario doesn't make much difference on file size, which is quite impressive, though I'm not sure I agree with the "hack" characterization pf the test.

>> ffmpeg -i in.mpg -acodec libfaac -ab 160k -crf 23.1 -vcodec libx264 -tune animation -preset faster -profile baseline -f mp4 -r 29.97 out.mp4
>> I was a bit surprised to find out that if I used -r 29.97 I would get a file with half the frames, but a larger size than if I hadn't done so. I'm sure I'm misunderstanding something, but is this the expected behavior? Here is the log data in case about the encodeing:
> What's the intention of -tune animation flag?

The flag is unrelated to the issue, but it was in the command I was using during the test, so I included it here. Probably should have left it out so as not to muddy the waters.

> To get video of desired bitrate, give that bitrate as a parameter.
> I'd suggest to not change framerate, and just tune encoder options to
> have satisfying output size or quality.
> Start from simply transcoding it without any options, just setting
> desired bitrate.

That is certainly the standard way to go about it. This was just an unexpected outcome of a test I was performing on a very specific use case and I wanted to make sure I wasn't misunderstanding the use of the frame rate flag and its affect on the final output.

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