[FFmpeg-devel] DNxHD and qmax

Michael Niedermayer michaelni at gmx.at
Thu Feb 2 20:38:10 CET 2012

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.


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No snowflake in an avalanche ever feels responsible. -- Voltaire
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