[FFmpeg-devel] [PATCH v2 6/6] avcodec/libsvtav1: support constant quality mode

[lance.lmwang at gmail.com]

On Sat, Sep 25, 2021 at 04:51:58PM +0300, Jan Ekström wrote:
> On Sat, Sep 25, 2021 at 4:35 PM <lance.lmwang at gmail.com> wrote:
> >
> > On Sat, Sep 25, 2021 at 03:35:53PM +0300, Jan Ekström wrote:
> > > On Thu, Sep 23, 2021 at 6:08 PM <lance.lmwang at gmail.com> wrote:
> > > >
> > > > On Thu, Sep 23, 2021 at 05:11:49PM +0300, Jan Ekström wrote:
> > > > > On Thu, Sep 23, 2021 at 4:46 PM Christopher Degawa <ccom at randomderp.com> wrote:
> > > > > >
> > > > > > On Sun, Sep 19, 2021 at 2:02 PM Christopher Degawa <ccom at randomderp.com>
> > > > > > wrote:
> > > > > >
> > > > > > >
> > > > > > >
> > > > > > > On Fri, Sep 17, 2021 at 9:28 PM <lance.lmwang at gmail.com> wrote:
> > > > > > >
> > > > > > >> From: Limin Wang <lance.lmwang at gmail.com>
> > > > > > >>
> > > > > > >> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> > > > > > >>
> > > > > > > As a note, I personally favor this patch over mine since I don't think
> > > > > > > `enable_tpl_la` is worth exposing to the user if its main role is to switch
> > > > > > > between crf and cqp
> > > > > > >
> > > > > >
> > > > > > Ping on this patch, this has been requested on SVT-AV1's side as well
> > > > >
> > > > > I think my further comments on the previous version were mostly to
> > > > > move off from the rc option for rate control, which has become more
> > > > > and more seemingly unnecessary (and different from most other encoders
> > > > > for no obvious reason).
> > > > >
> > > > > The only option that with a quick look doesn't match just setting
> > > > > quantizer|bit rate|CRF is "cvbr", but it doesn't seem to be impossible
> > > > > to either rework "rc" for it, or to utilize a separate option for it.
> > > >
> > > > Do you think it's OK to remove the rc option? to match other encoders,
> > > > We can choose the rate control by the related parameters like:
> > > >
> > > > if (crf >= 0)
> > > >     choose crf rate control;
> > > > else if (bitrate > 0)
> > > >     choose cvbr rate control;
> > > > else if (cqp >=0 )
> > > >     choose cqp rate control;
> > > >
> > >
> > > In general that is the idea, yes (except bit rate would mean either
> > > vbr or cvbr). It would be nice to follow whatever is the default on
> > > SVT-AV1's side by default, and then if the user specifies a rate
> > > control mode that is not the default, his selection is honored. Not
> > > sure what the best way for that is to be honest. Possibly the style of
> > > setting AVCodecDefault a la libx265?
> > >
> > > For the rc option, given how much SVT-AV1 itself is in flux, I would
> > > be OK with removing the option, or making it an option that decides
> > > between cvbr and vbr (essentially making it "VBR bit rate control
> > > mode"). I wish cvbr would instead be something like VBV/HRD elsewhere,
> > > so we could just utilize maxrate&bufsize for controlling it, instead
> > > of having it as another discrete rate control mode.
> >
> > Yes, I think it's preferable to use utilize maxrate&bufsize to control
> > cbr and vbr as most of encoder. Then I'll follow this direction to update
> > the patch.
> >
> 
> Unfortunately that was just wishful thinking :) .
> 
> Unless you can set the buffer size and max rate in SVT-AV1, of course.
> With the limited looking I've done CVBR just uses the bit rate for
> each GOP instead of average over the whole clip.

As it's not very clear yet, so I'll not update this patch anymore.

> 
> > >
> > > As these things change, I also hope that SVT-AV1 will soon get a
> > > key=value style of option API, that way the wrapper will not have to
> > > be updated constantly according to the changes in the library :) . As
> > > I feel SVT-AV1 will be changed quite a bit in the future (due to its
> > > recent age).
> > >
> >
> > Yes, it's good to add svtav1-opts so that we can utilize the update options
> > directly.
> >
> 
> Let's go with -params ;) Since that is what modules seem to have
> standardized on (x264|x265|rav1e|aom) :)
> 
> But that is anyways in the future, since SVT-AV1 doesn't have such an
> API yet (as far as I know).

I think I have tried to add new options half year again, there are willing to
hold and let to wait for the params API.

> 
> Jan
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-- 
Thanks,
Limin Wang