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

[Timothy Gu]

On Fri, Nov 1, 2013 at 4:27 AM, Stefano Sabatini <stefasab at gmail.com> wrote:
> 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.

If you test with 0, 1, and 10, they will produce the same effect as
faac does not support 0-9 (it just clips to 10).

Timothy