[FFmpeg-devel] DNxHD and qmax

Joseph Artsimovich joseph at mirriad.com
Tue Feb 7 16:51:53 CET 2012

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.
Patch is attached.

Joseph Artsimovich
Senior C++ Applications Developer
MirriAd Ltd

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