[Ffmpeg-devel] h263+: size of encoded frames after opening ffmpeg

[Michael Niedermayer]

Hi

On Fri, Jan 19, 2007 at 11:23:59AM +0100, Martin wrote:
> Hi,
> 
> Michael Niedermayer wrote:
> > Hi
> > 
> > On Wed, Jan 17, 2007 at 11:14:40AM +0100, Martin wrote:
> > [...]
> > 
> >>>>Even better, is there a
> >>>>possibility to change the bitrate without closing and reopening ffmpeg?
> >>>
> >>>
> >>>you can set the quality of frames which affects the bitrate,
> >>>closing and reopening within the same stream is generally not allowed
> >>>doing so means you are on your own
> >>
> >>Ok, how can I set the quality within the same stream without closing and
> >>reopening? I tried to set the AVCodecContext.crf parameter but it
> >>doesn't seem to have any effect on quality and size of outputted frames.
> >>Is there another parameter which I can use?
> > 
> > 
> > AVFrame.quality 
> > and set CODEC_FLAG_QSCALE
> 
> Thank you very much, that worked. How is the relationship between
> quality and bitrate? Is there a formula which expresses it?

besides encode at quality X and look at the bitrate, no but theres some
approximation, and that is that quality and bitrate are approximatly
inversly proportional so double the quality variable and bitrate should
be approximately cut in half


> 
> What is the default quality used, if no quality is specified and the
> flag is not set?

selected dynamically by ratecontrol.c based on many things (see the source)

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

There will always be a question for which you do not know the correct awnser.
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