[FFmpeg-devel] [PATCH] Change libaom default to crf=28.

[Elliott Karpilovsky]

It appears that CRF=32 is a better default, since the scale is
different from other codecs. I will start a new thread.

On Tue, Aug 20, 2019 at 5:31 PM Elliott Karpilovsky <elliottk at google.com> wrote:
>
> I believe the documentation is out of date. I added some debug
> statements and verified that variable was being used to pull CRF
> values when AOM_Q mode is set. I have
> https://aomedia-review.googlesource.com/c/aom/+/94104 out to update
> the documentation.
>
>
> On Fri, Aug 16, 2019 at 10:59 AM James Zern
> <jzern-at-google.com at ffmpeg.org> wrote:
> >
> > Hi,
> >
> > On Thu, Aug 15, 2019 at 1:22 PM elliottk
> > <elliottk-at-google.com at ffmpeg.org> wrote:
> > >
> > > Current default is 256kbps, which produces inconsistent
> > > results (too high for low-res, too low for hi-res).
> > > Use CRF instead, which will adapt.
> > > ---
> > >  libavcodec/libaomenc.c | 9 +++++----
> > >  1 file changed, 5 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/libavcodec/libaomenc.c b/libavcodec/libaomenc.c
> > > index 9b4fb3b4eb..621e897672 100644
> > > --- a/libavcodec/libaomenc.c
> > > +++ b/libavcodec/libaomenc.c
> > > @@ -575,10 +575,11 @@ static av_cold int aom_init(AVCodecContext *avctx,
> > >          if (enccfg.rc_end_usage == AOM_CQ) {
> > >              enccfg.rc_target_bitrate = 1000000;
> > >          } else {
> > > -            avctx->bit_rate = enccfg.rc_target_bitrate * 1000;
> > > +            enccfg.rc_end_usage = AOM_Q;
> >
> > Unless the docs are out of date this should be AOM_CQ level since crf
> > is mapped to that control [1].
> >
> > > +            ctx->crf = 28;
> > >              av_log(avctx, AV_LOG_WARNING,
> > > -                   "Neither bitrate nor constrained quality specified, using default bitrate of %dkbit/sec\n",
> > > -                   enccfg.rc_target_bitrate);
> > > +                   "Neither bitrate nor constrained quality specified, using default CRF of %d\n",
> > > +                   ctx->crf);
> > >          }
> > >      }
> > >
> >
> > [1] https://aomedia.googlesource.com/aom/+/refs/heads/master/aom/aomcx.h#221
> > "For this value to be used aom_codec_enc_cfg_t::rc_end_usage must be
> > set to #AOM_CQ."
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