[FFmpeg-devel] DNxHD and qmax

Michael Niedermayer michaelni at gmx.at
Tue Feb 7 21:56:55 CET 2012

On Tue, Feb 07, 2012 at 03:51:53PM +0000, Joseph Artsimovich wrote:
> On 03/02/2012 07:57, Baptiste Coudurier wrote:
> >On 2/2/12 11:38 AM, Michael Niedermayer wrote:
> >>On Thu, Feb 02, 2012 at 09:55:21AM +0000, Joseph Artsimovich wrote:
> >>>On 02/02/2012 03:52, Michael Niedermayer wrote:
> >>>>On Wed, Feb 01, 2012 at 11:13:46AM +0000, Joseph Artsimovich wrote:
> >>>>>The default value for qmax in FFMpeg is 31, with FFmpeg's DNxHD
> >>>>>encoder actually enforcing it. Now, enforcing qmax in a CBR codec
> >>>>>makes no sence, as no one wants encoding to fail just because the
> >>>>>minimum allowed quality specified by qmax doesn't fit into the given
> >>>>>bitrate. The DNxHD specification actually specifies 1024 as the
> >>>>>maximum quantization scale factor.
> >>>>>
> >>>>>Should I submit a patch making the DNxHD encoder ignore qmax?
> >>>>the default value can be overriden, see libx264.c for example
> >>>>that seems more flexible as the user then still can set it if he
> >>>>really wants to
> >>>That's easy to implement, however I would rather not give users
> >>>ability to set qmax for CBR codecs, as it means giving them a rope
> >>>to hang themselves on. I don't see any other uses for that feature.
> >>hmm, the encoder could try to honor the qmax and only if that fails
> >>ignore it to achive the bitrate requirements
> >>
> >>anyway, unless baptiste disagrees iam happy to apply whatever patch
> >>you consider to be the correct solution.
> >Let the user specify qmax.
> Done.
> Patch is attached.

applied (will push if it passes tests)



Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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