[Ffmpeg-devel] qprd and frames being stuck at high quants

[Michael Niedermayer]

Hi

On Thu, Nov 02, 2006 at 11:42:53AM -0800, Corey Hickey wrote:
> Michael Niedermayer wrote:
> >Hi
> >
> >there where some bugreports aout $subj a long time ago, but all the
> >sample videos seem to have dissapeared, if that bug is still happening
> >for anyone, then please upload a sample source file which causes it
> >(with command line options ...)
> 
> No problem with high quantizers so far, but I did find a possible small 
> usability bug. When encoding with vqmin=1:lmin=1, qprd appears to be 
> nearly preventing the use of quantizer=1. At very high requested 
> bitrate, this makes the output bitrate and PSNR much lower.
> 
> --------------------- without qprd -------------------
> for i in 1:turbo 2 ; do
>   mencoder matrix.vob -nosound -vf crop=718:356:0:60,scale=640:272 \
>   -ovc lavc -lavcopts \
>   vcodec=mpeg4:vbitrate=16000:psnr:mbd=2:vqmin=1:lmin=1:vpass=$i \
>   -ofps 24000/1001 -o test.avi -frames 2400
> done
> 
> Video stream: 7794.736 kbit/s
> PSNR: Y:49.91, Cb:50.19, Cr:50.72, All:50.08
> 
> ---------------------- with qprd ---------------------
> (same as above, but adding qprd to lavcopts)
> 
> Video stream: 3914.993 kbit/s
> PSNR: Y:45.18, Cb:46.26, Cr:45.81, All:45.44
> 
> 
> When I play the output video with -lavdopts debug=1, the lowest 
> frame-level quantizer I see is 2. If I use debug=16, I see three blocks 
> with a quantizer of 1, out of the entire video.
> 
> I can upload a sample video if you need, but I think it's reproducible 
> with any source.
> 
> 
> I know this is a rather minor issue, since encoding at such high 
> bitrates is rare, but I still thought it worth pointing out.

retry with mblmin=lmin

QP_RD activates adaptive quantization, which uses mblmin/max

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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