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

[Tom Evans]

On Fri, Jan 18, 2013 at 3:37 PM, James Miller <gajs-f0el at dea.spamcon.org> wrote:
> Attempting to implement Carl's suggestions, I tried this as a first pass:
> ffmpeg -y -i infile.mkv -pass 1 -acodec libvorbis -ab 48k -ac 2 -vcodec
> libtheora -b 100k -threads 0 outfile.ogv and got the following output:
>
> ffmpeg version 0.8.4-4:0.8.4-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the
> Libav developers
>   built on Nov  6 2012 16:50:25 with gcc 4.6.3
> *** THIS PROGRAM IS DEPRECATED ***

You've been fooled, this is not ffmpeg, it is a fork of ffmpeg, and
you're unlikely to get support for it on here. The fault is your
distributor, who decided to switch to the fork. It is very easy to
build the latest ffmpeg from source, which is what is supported on
this mailing list.

> <snip>
> The lossless infile.mkv is 491 MB in size, while outfile.ogv winds up being
> 81 MB. That outfile, for some reason, is slightly larger than the file I
> produced using the 1 pass encoding with the errant -crf option and no -b
> option set: that outfile.ogv came in at 73 MB (command line ffmpeg -i
> infile.mkv -r 13 -acodec libvorbis -ab 48k -ac 2 -vcodec libtheora -preset
> slow -wpredp 0 -crf 22 -threads 0 outfile.ogv). I can't detect any
> difference in quality between the two files: both are of acceptable quality
> for my uses.
>

If you aren't trying to maximise the available space, eg by ensuring
that you use every single byte available on a DVD, a target bitrate is
not really worth it, and hence by extension, 2 pass is not worth it.

Experiment with the crf option until you find a quality level you are
happy with. A higher crf will result in a lower quality, lower bitrate
file, a lower crf will increase the quality and bitrate.

And use ffmpeg, not the avconv fork!

Cheers

Tom