[FFmpeg-devel] [FFmpeg-cvslog] lavc/qsvenc: add VDENC support for H264

[Li, Zhong]

> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> Of Carl Eugen Hoyos
> Sent: Friday, January 11, 2019 10:39 AM
> To: FFmpeg development discussions and patches
> <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [FFmpeg-cvslog] lavc/qsvenc: add VDENC
> support for H264
> 
> 2019-01-11 3:28 GMT+01:00, Li, Zhong <zhong.li at intel.com>:
> >> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On
> Behalf
> >> Of Carl Eugen Hoyos
> >> Sent: Friday, January 11, 2019 1:06 AM
> >> To: ffmpeg-devel at ffmpeg.org
> >> Subject: Re: [FFmpeg-devel] [FFmpeg-cvslog] lavc/qsvenc: add VDENC
> >> support for H264
> >>
> >> 2019-01-10 14:51 GMT+01:00, Linjie Fu <git at videolan.org>:
> >>
> >> > +#if QSV_HAVE_VDENC
> >> > +    { "low_power", "enable low power mode(experimental: many
> >> > +limitations by
> >> > mfx version, BRC modes, etc.)", OFFSET(qsv.low_power),
> >> > AV_OPT_TYPE_BOOL, {
> >> > .i64 =  0 }, 0, 1, VE},
> >> > +#endif
> >>
> >> This seems wrong to me: The visibility of an option should probably
> >> not depend on configuration details (the effect can of course depend
> >> on many details).
> >>
> >> Carl Eugen
> >
> > That's is just a remind that this feature has some limitations. The
> > configures are just to make driver to support this feature.
> > In ffmpeg level, the only thing we should do IMHO is to query
> > MSDK/Driver capability and report an error message if not supported.
> > And it was done:
> >
> https://github.com/FFmpeg/FFmpeg/blob/395e8a53fa0266f26581f3e9752b
> 0dbc
> > 93998a90/libavcodec/qsvenc.c#L376
> 
> That is probably helpful, but the issue I try to explain is unrelated to the
> brokenness of the option:
> Now, in some cases FFmpeg shows the option and in other cases it does not.
> I believe that instead, the option should always be shown, even if it does not
> work.

That is a big topic since I see many components are doing this. E.g; we can find some options of libx264 and nvenc are hided too.
Personally speaking I like current way: if the implementation of an option is not built-in, it is not necessary to show the option, else it is really confusing that this option can't work at any case.
But I am open to your suggestion, and looking forward more comments from you and others. (If we get alignment, we need to clear up many options, not only this one).