[FFmpeg-devel] [PATCH] Changed max bitrate for VBV mode (according to Ivan Uskow)

Michael Niedermayer michael at niedermayer.cc
Fri Aug 14 10:50:49 CEST 2015


On Fri, Aug 14, 2015 at 10:42:38AM +0200, Sven Dueking wrote:
> 
> 
> > -----Urspr√ľngliche Nachricht-----
> > Von: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] Im Auftrag
> > von Michael Niedermayer
> > Gesendet: Freitag, 14. August 2015 10:32
> > An: FFmpeg development discussions and patches
> > Betreff: Re: [FFmpeg-devel] [PATCH] Changed max bitrate for VBV mode
> > (according to Ivan Uskow)
> > 
> > On Fri, Aug 14, 2015 at 07:37:08AM +0200, Sven Dueking wrote:
> > >
> > >
> > > > -----Urspr√ľngliche Nachricht-----
> > > > Von: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] Im
> > > > Auftrag von Michael Niedermayer
> > > > Gesendet: Donnerstag, 13. August 2015 17:41
> > > > An: FFmpeg development discussions and patches
> > > > Cc: Sven Dueking
> > > > Betreff: Re: [FFmpeg-devel] [PATCH] Changed max bitrate for VBV
> > mode
> > > > (according to Ivan Uskow)
> > > >
> > > > On Thu, Aug 13, 2015 at 11:30:45AM +0100, Sven Dueking wrote:
> > > > > From: Sven Dueking <sven at nablet.com>
> > > > >
> > > > > ---
> > > > >  libavcodec/qsvenc.c | 6 +++++-
> > > > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/libavcodec/qsvenc.c b/libavcodec/qsvenc.c index
> > > > > 57f5fe4..b56e4b4 100644
> > > > > --- a/libavcodec/qsvenc.c
> > > > > +++ b/libavcodec/qsvenc.c
> > > > > @@ -118,10 +118,14 @@ static int init_video_param(AVCodecContext
> > > > > *avctx, QSVEncContext *q)
> > > > >
> > > > >      switch (q->param.mfx.RateControlMethod) {
> > > > >      case MFX_RATECONTROL_CBR:
> > > > > +	q->param.mfx.InitialDelayInKB = avctx-
> > > > >rc_initial_buffer_occupancy / 1000;
> > > > > +        q->param.mfx.TargetKbps       = avctx->bit_rate / 1000;
> > > > > +        q->param.mfx.MaxKbps          = avctx->bit_rate / 1000;
> > > > > +        break;
> > > > >      case MFX_RATECONTROL_VBR:
> > > > >          q->param.mfx.InitialDelayInKB = avctx-
> > > > >rc_initial_buffer_occupancy / 1000;
> > > > >          q->param.mfx.TargetKbps       = avctx->bit_rate / 1000;
> > > > > -        q->param.mfx.MaxKbps          = avctx->bit_rate / 1000;
> > > > > +        q->param.mfx.MaxKbps          = avctx->rc_max_rate /
> > 1000;
> > > >
> > > > why is rc_max_rate not used for MFX_RATECONTROL_CBR ?
> > >
> > > Hi Michael,
> > >
> > > Ivan is on vacation and I did the fix according to his last command :
> > >
> > > "This correct for MFX_RATECONTROL_CBR but a bug for
> > MFX_RATECONTROL_VBR.
> > > Will fixed later. For any case part of ratecontrol setup should be
> > > re-designed to support more advanced LA rate contol"
> > >
> > > The Intel Documentation states that :
> > >
> > > For variable bitrate control, the MaxKbps parameter specifies the
> > > maximum bitrate at which the encoded data enters the Video Buffering
> > > Verifier (VBV) buffer.
> > >
> > > And for CBR the target bitrate and max bitrate should be equal to
> > > archive a bitrate that is near a desired target for streaming (no
> > > peaks etc.)
> > 
> > In the code there is this:
> > 
> >     } else if (avctx->rc_max_rate == avctx->bit_rate) {
> >         q->param.mfx.RateControlMethod = MFX_RATECONTROL_CBR;
> >         ratecontrol_desc = "constant bitrate (CBR)";
> > 
> > assuming thats how CBR is set, the variables are equal and the special
> > case is not needed am i missing something ?
> 
> No, you are right. I missed that. So max_rate and bit_rate have the same
> value..  means you can ignore my patch or keep it for readability.

the patch also changes MaxKbps for
MFX_RATECONTROL_VBR

that change looks correct, do you agree ?
if so please resubmit a patch with only it

thanks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
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