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

[Sven Dueking]

> -----Ursprüngliche 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:
> >
> >
> > > -----Ursprüngliche 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.

> 
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> 
> The misfortune of the wise is better than the prosperity of the fool.
> -- Epicurus