[FFmpeg-devel] [PATCH] Adds support for constant quality mode in VP9.

[Debargha Mukherjee]

Comments inline.


On Thu, Aug 21, 2014 at 7:03 PM, James Zern <jzern at google.com> wrote:

> On Thu, Aug 21, 2014 at 4:33 PM, Deb Mukherjee <debargha at google.com>
> wrote:
> > Changes in the parameter mapping for libvpx to support the constant
> > quality mode in VP9. The assumption in the patch is that if crf is
> > provided but bitrate is 0, then the 'constant quality' mode of VP9
> > is used. However if both are present, the 'constrained quality' mode
> > is used as before.
> > ---
> >  libavcodec/libvpxenc.c | 20 ++++++++++++++------
> >  1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/libavcodec/libvpxenc.c b/libavcodec/libvpxenc.c
> > index 830a793..a6e5392 100644
> > --- a/libavcodec/libvpxenc.c
> > +++ b/libavcodec/libvpxenc.c
> > @@ -300,10 +300,17 @@ static av_cold int vpx_init(AVCodecContext *avctx,
> >          enccfg.g_pass = VPX_RC_ONE_PASS;
> >
> >      if (avctx->rc_min_rate == avctx->rc_max_rate &&
> > -        avctx->rc_min_rate == avctx->bit_rate && avctx->bit_rate)
> > +        avctx->rc_min_rate == avctx->bit_rate && avctx->bit_rate) {
> >          enccfg.rc_end_usage = VPX_CBR;
> > -    else if (ctx->crf)
> > +    } else if (ctx->crf >= 0) {
>
> Is 0 only meaningful for VPX_Q?
>

yes.
If crf is specified and bitrate is 0 (stands for don't care), then  VPX_Q
is used.


> >          enccfg.rc_end_usage = VPX_CQ;
> > +#if CONFIG_LIBVPX_VP9_ENCODER
> > +        if (!avctx->bit_rate && avctx->codec_id == AV_CODEC_ID_VP9)
> > +            enccfg.rc_end_usage = VPX_Q;
> > +#endif
> > +        av_log(avctx, AV_LOG_INFO, "%s usage set with cq=%d\n",
> > +               enccfg.rc_end_usage == VPX_CQ ? "VPX_CQ" : "VPX_Q",
> ctx->crf);
>
> This gets dumped at debug loglevel, probably not necessary here.
>

Removed.


>
> > +    }
> >
> >      if (avctx->bit_rate) {
> >          enccfg.rc_target_bitrate = av_rescale_rnd(avctx->bit_rate, 1,
> 1000,
> > @@ -311,7 +318,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
> >      } else {
> >          if (enccfg.rc_end_usage == VPX_CQ) {
> >              enccfg.rc_target_bitrate = 1000000;
> > -        } else {
> > +        } else if (enccfg.rc_end_usage != VPX_Q) {
> >              avctx->bit_rate = enccfg.rc_target_bitrate * 1000;
> >              av_log(avctx, AV_LOG_WARNING,
> >                     "Neither bitrate nor constrained quality specified,
> using default bitrate of %dkbit/sec\n",
> > @@ -324,7 +331,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
> >      if (avctx->qmax >= 0)
> >          enccfg.rc_max_quantizer = avctx->qmax;
> >
> > -    if (enccfg.rc_end_usage == VPX_CQ) {
> > +    if (enccfg.rc_end_usage == VPX_CQ || enccfg.rc_end_usage == VPX_Q) {
>
> When was this introduced? You should be careful with it's use, someone
> could be building with an old VP8-only lib.
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>



-- 
Debargha Mukherjee, Ph.D.
Staff Software Engineer,
Google, Inc.
Email: debargha at google.com
Phone: 650-253-0775 (desk), 408-234-5956 (cell)