[FFmpeg-user] formula for transcoding to ogv, shrinking an mkv

[James Miller]

While awaiting a response to this query I did some further 
experimentation. I was able to come up with a new incantation which gives 
smaller output files--I think mainly owing to a slower frame rate option 
(-r 13) I introduced. That incantation is as follows:

ffmpeg -i infile.mkv -r 13 -acodec libvorbis -ab 48k -ac 2 -vcodec 
libtheora -preset slow -wpredp 0 -crf 22 -threads 0 outfile.ogv

Again, should anyone see any errors in or problems with this incantation, 
or if anyone can offer improvements, please do so. I would be happy to 
learn more about this utility and its workings.

James

On Mon, 14 Jan 2013, James wrote:

> I do some screencasting, that involves both video and audio capture, using 
> ffmpeg's x11grab. At the same time, I have upload limits at the site where I 
> wish to host these screencasts. On doing some reading and making a few 
> consultations, I decided I should record my screencasts in a lossless format, 
> then convert and shrink the resulting files prior to uploading. I came across 
> a good incantation for converting and shrinking to flv: the resulting files 
> are actually about one tenth the size of the original, lossless ones--just 
> about the ideal proportion. Now, though, I'd like to try and develop a 
> similar formula for converting and shrinking to ogv. The following 
> incantation, which I developed by trial and error, gives a result close to 
> what I need:
>
> ffmpeg -i infile.mkv -acodec libvorbis -ab 48k -ac 2 -vcodec libtheora 
> -preset slow -wpredp 0 -crf 22 -threads 0 outfile.ogv
>
> But that results in a file about one-sixth the size of the lossless original, 
> while I'd like to make the outfile size more like one tenth. Can anyone offer 
> suggestions on yet further shrinking the resulting ogv file? Also, please 
> feel free to offer any corrections to the incantation I've come up with: I 
> (as may be clear) have a rather poor understanding of ffmpeg.
>
> Thanks,
> James
>