[FFmpeg-devel] [PATCH] Allow to modify max qp configuration parameter in libvpx without reseting the encoder

[Anton Khirnov]

Quoting Lynne (2022-03-16 13:37:55)
> 16 Mar 2022, 13:13 by danilchap-at-google.com at ffmpeg.org:
> 
> > On Mon, Mar 14, 2022 at 4:28 PM Jan Ekström <jeebjp at gmail.com> wrote:
> >
> >>
> >> On Mon, Mar 14, 2022 at 3:05 PM Danil Chapovalov
> >> <danilchap-at-google.com at ffmpeg.org> wrote:
> >> >
> >> > ---
> >>
> >> Probably something a la
> >>
> >> avcodec/libvpxenc: enable dynamic quantizer reconfiguration
> >>
> >> ?
> >>
> >
> > Thank you, resubmitted with new title
> >
> >>
> >> >  libavcodec/libvpxenc.c | 7 +++++++
> >> >  1 file changed, 7 insertions(+)
> >> >
> >> > diff --git a/libavcodec/libvpxenc.c b/libavcodec/libvpxenc.c
> >> > index 8f94ba15dc..45baeed435 100644
> >> > --- a/libavcodec/libvpxenc.c
> >> > +++ b/libavcodec/libvpxenc.c
> >> > @@ -1658,6 +1658,13 @@ static int vpx_encode(AVCodecContext *avctx, AVPacket *pkt,
> >> >                  flags |= strtoul(en->value, NULL, 10);
> >> >              }
> >> >
> >> > +            en = av_dict_get(frame->metadata, "max-quantizer", NULL, 0);
> >> > +            if (en) {
> >> > +                struct vpx_codec_enc_cfg cfg = *enccfg;
> >> > +                cfg.rc_max_quantizer = strtoul(en->value, NULL, 10);
> >> > +                vpx_codec_enc_config_set(&ctx->encoder, &cfg);
> >> > +            }
> >> > +
> >>
> >> There is side data already defined for quantizers, AVVideoEncParams /
> >> AV_FRAME_DATA_VIDEO_ENC_PARAMS .
> >>
> >> In other words, this should be handled in a similar manner to ROI, not
> >> as an ad-hoc metadata key in the AVFrame.
> >>
> >
> > I've checked struct AVVideoEncParams, it doesn't look fitting: it
> > contains exact qp (plus qp per plane), while my patch suggests
> > changing max-qp limit for current and following frames.
> > AVVideoEncParams also has some extra fields that I'm unsure how to
> > handle (they are unrelated to what I'm trying to do),
> > I haven't found any other struct that would contain something like max qp.
> > What is ROI? What code can I use as an example of your suggestion?
> >
> 
> If the encoder is operating under bitrate mode, then I think it would
> be fine to interpret the qp field as a max qp field.
> IIRC Youtube run libvpx and libaom under constant bitrate mode and
> adjust the max quantizer per frame, because no one can fix the
> rate control system of either library.

Why not just update AVCodecContext.qmax?

-- 
Anton Khirnov