[FFmpeg-devel] [PATCH] doc/encoders: add libfaac encoder documentation

[Stefano Sabatini]

On date Thursday 2013-10-31 17:56:08 -0700, Timothy Gu encoded:
> On Thu, Oct 31, 2013 at 1:42 AM, Stefano Sabatini <stefasab at gmail.com> wrote:
> > On date Wednesday 2013-10-30 19:53:29 -0700, Timothy Gu encoded:
> >> On Oct 30, 2013 6:26 AM, "Stefano Sabatini" <stefasab at gmail.com> wrote:
> 
> >> > + at item q (@emph{-q})
> >> > +Enable VBR mode, and set constant quality value as an integer.
> >> > +
> >> > +This option is valid only using the @command{ffmpeg} command-line
> >> > +tool. The value is expressed in QP units, the higher the value the
> >> > +higher the quality. A reasonable range for the option value is
> >> > +[10-500].
> >>
> >> The valid range for...
> >
> > Not exactly, since it will accept any non-negative value, but
> > reasonable quality starts with 10. I didn't check libfaac
> > documentation properly, I think this is already (much) better than
> > nothing.
> 
> FAAC only supports 10-500.
> http://manpages.ubuntu.com/manpages/raring/man1/faac.1.html

Values from 0 to 1,000,000 are accepted, but values greater than 500
produces the same output size.

A value of 0 is accepted, and produces very low quality. A negative
value will not set VBR mode, since it will not enable the +qscale flag.

The following outputs have been generated with the command:
ffmpeg -i slow.flv -vn -c:a libfaac -profile:a aac_low -q:a $qp -y out$qp.m4a

ls -lh out*.m4a
-rw-r--r-- 1 stefano stefano 257K nov  1 11:57 out+0.m4a
-rw-r--r-- 1 stefano stefano 2,3M nov  1 10:22 out+10000.m4a
-rw-r--r-- 1 stefano stefano 2,3M nov  1 10:22 out+1000.m4a
-rw-r--r-- 1 stefano stefano 1,3M nov  1 10:22 out+100.m4a
-rw-r--r-- 1 stefano stefano 257K nov  1 10:21 out+1.m4a
-rw-r--r-- 1 stefano stefano 395K nov  1 10:21 out+20.m4a
-rw-r--r-- 1 stefano stefano 2,3M nov  1 10:22 out+500.m4a
-rw-r--r-- 1 stefano stefano 899K nov  1 10:22 out+50.m4a

I'll push soon with a few more changes. Feel free to suggest more
tweaks.
-- 
FFmpeg = Fancy and Fabulous Mastering Pitiful Evil Generator