[FFmpeg-devel] [PATCH 3/4] vaapi_encode_h265: Query encoding block sizes and features

[Fu, Linjie]

> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Mark Thompson
> Sent: Sunday, March 8, 2020 00:31
> To: ffmpeg-devel at ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH 3/4] vaapi_encode_h265: Query
> encoding block sizes and features
> 
> On 05/03/2020 05:13, Fu, Linjie wrote:
> >> -----Original Message-----
> >> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> >> Mark Thompson
> >> Sent: Thursday, March 5, 2020 08:25
> >> To: ffmpeg-devel at ffmpeg.org
> >> Subject: [FFmpeg-devel] [PATCH 3/4] vaapi_encode_h265: Query
> encoding
> >> block sizes and features
> >>
> >> ---
> >> Requires <https://github.com/intel/libva/pull/385>.  That isn't upstream,
> so
> >> this will need to wait for that and then get at least a fix to the version
> >> numbering before applying.
> >
> > The query looks good to me since I'm suffering from the differences of
> default
> > parameters allowed for VDENC and VMEPAK in media-driver while adding
> support
> > for low power encoding [1] for VAAPI.
> >
> > However got several questions:
> >
> > 1. Why not include PPS parameters as well? There are some differences in
> > cu_qp_delta_enabled_flag and diff_cu_qp_delta_depth supported for
> VAEntrypointEncSliceLP.
> 
> Support for cu_qp_delta_enabled_flag is implied by the presence of non-
> CQP RC modes (maybe I should add a comment saying that explicitly?).
> 
> The possible range of diff_cu_qp_delta_depth is set by
> min_cu_qp_delta_block_size_minus3, since the variable you actually want to
> define is Log2MinCuQpDeltaSize.  (So for example that would be 1 if the
> smallest block supporting a qp_delta is 16x16 (Log2MinCuQpDeltaSize = 4),
> and then depth could be up to 2 on 64x64 CTBs or 1 on 32x32 CTBs.)

Yes you are right, this should be not related with LP,  setting the depth would
make sense. 
Log2MinCuQpDeltaSize = CtbLog2SizeY − diff_cu_qp_delta_depth;

> > 2. Would it be better to only involve the variable parameters for sps/pps... ?
> This is
> > what PR 379 [2] (unfinished) intended to do.
> 
> I'm not sure what you mean by this question - all of these are variable
> parameters in SPS/PPS.
>
> > 3. The suggested value of SAO enable flag could also be 1 in corresponding
> code in
> > media-driver, which would provide 3% BD-Rate improvement with no fps
> penalty
> > based on previous experiment with FFmpeg VAAPI.
> 
> Huh, nice.  That never worked in Gen 9, so I guess that's another difference
> which needs the query information to express.
> 
> > 4. There is separate media_libva_caps for gen11 and gen12, maybe need
> further update
> > or centralization for the code in driver. (not tested yet, will do later)
> 
> Since the documentation has not been released this needs someone from
> Intel to define what the capabilities actually are.  As I wrote in the PR against
> iHD, all I have are guesses based on what I can observe working (or not).
> 

I'll sync with media-driver and try to get capabilities for each platform.
Thanks for the PRs in libva and iHD.

- Linjie