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

Michael Niedermayer michael at niedermayer.cc
Fri Aug 14 10:32:24 CEST 2015


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 ?

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

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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