Re: [FFmpeg-devel] [PATCH v1] lavc/vaapi_encode_av1: Add qp option explicitly to set base q index

["Xiang, Haihao" <haihao.xiang-at-intel.com@ffmpeg.org>]

On Ma, 2023-11-27 at 13:36 +0000, Mark Thompson wrote:
> On 27/11/2023 00:58, fei.w.wang-at-intel.com@ffmpeg.org wrote:
> > From: Fei Wang <fei.w.wang@intel.com>
> > 
> > Keep same way with librav1e/libsvtav1/qsv_av1.. to make it more
> > acceptable instead of using global option "-global_quality".
> > 
> > Fix #10615
> > 
> > Signed-off-by: Fei Wang <fei.w.wang@intel.com>
> > ---
> >   doc/encoders.texi             | 1 +
> >   libavcodec/vaapi_encode_av1.c | 6 ++++++
> >   2 files changed, 7 insertions(+)
> > 
> > diff --git a/doc/encoders.texi b/doc/encoders.texi
> > index 27a9acf076..2cffc32daf 100644
> > --- a/doc/encoders.texi
> > +++ b/doc/encoders.texi
> > @@ -4079,6 +4079,7 @@ Each encoder also has its own specific options:
> >   @table @option
> >   
> >   @item av1_vaapi
> > +@option{qp} sets the value of @emph{base_q_index}.
> >   @option{profile} sets the value of @emph{seq_profile}.
> >   @option{tier} sets the value of @emph{seq_tier}.
> >   @option{level} sets the value of @emph{seq_level_idx}.
> > diff --git a/libavcodec/vaapi_encode_av1.c b/libavcodec/vaapi_encode_av1.c
> > index 5a9ff0f798..2e327fec5a 100644
> > --- a/libavcodec/vaapi_encode_av1.c
> > +++ b/libavcodec/vaapi_encode_av1.c
> > @@ -79,6 +79,7 @@ typedef struct VAAPIEncodeAV1Context {
> >       int cdef_param_size;
> >   
> >       /** user options */
> > +    int qp;
> >       int profile;
> >       int level;
> >       int tier;
> > @@ -786,6 +787,9 @@ static av_cold int vaapi_encode_av1_init(AVCodecContext
> > *avctx)
> >           return AVERROR(EINVAL);
> >       }
> >   
> > +    if (priv->qp > 0)
> > +        ctx->explicit_qp = priv->qp;
> > +
> >       ret = ff_vaapi_encode_init(avctx);
> >       if (ret < 0)
> >           return ret;
> > @@ -864,6 +868,8 @@ static av_cold int vaapi_encode_av1_close(AVCodecContext
> > *avctx)
> >   static const AVOption vaapi_encode_av1_options[] = {
> >       VAAPI_ENCODE_COMMON_OPTIONS,
> >       VAAPI_ENCODE_RC_OPTIONS,
> > +    { "qp", "Base q index (for P-frames; scaled by qfactor/qoffset for
> > I/B)",
> > +      OFFSET(qp), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 255, FLAGS },
> >       { "profile", "Set profile (seq_profile)",
> >         OFFSET(profile), AV_OPT_TYPE_INT,
> >         { .i64 = AV_PROFILE_UNKNOWN }, AV_PROFILE_UNKNOWN, 0xff, FLAGS,
> > "profile" },
> 
> Disagree; QP is not a concept in AV1. 

Yes, it not a concept in AV1.

nvenc h264/hevc/av1 encoders provide the same qp option:

libavcodec/nvenc_av1.c:    { "qp",           "Constant quantization parameter
rate control method",
libavcodec/nvenc_h264.c:    { "qp",           "Constant quantization parameter
rate control method",
libavcodec/nvenc_hevc.c:    { "qp",           "Constant quantization parameter
rate control method",

May we provide the same qp option for vaapi h264/hevc/av1 encoders too? User
will be able to use same options when using these encoders.

Thanks
Haihao


>  Further, your examples from other encoders do not have a consistent view of
> what it should mean.
> 
> librav1e.c:
> 
>      { "qp", "use constant quantizer mode", OFFSET(quantizer),
> AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 255, VE },
> 
> 0-255 is presumably the base_q_idx scale.
> 
> libsvtav1.c:
> 
>      { "qp", "Initial Quantizer level value", OFFSET(qp),     
> AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 63, VE },
> 
> 0-63 is presumably the H.26x-qp-ish scale used by some VP9/AV1 encoders which
> maps nonlinearly to the internal scale.
> 
> qsv_av1 doesn't seem to have such an option.
> 
> Thanks,
> 
> - Mark
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