[Ffmpeg-devel] qprd and frames being stuck at high quants
Thu Nov 2 23:21:43 CET 2006
Corey Hickey wrote:
> Michael Niedermayer wrote:
>>>> 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
>>> 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
> Do you mean mbqmin? mblmin doesn't seem to exist, though I haven't
> looked at the source yet.
Ok, I made a patch for mplayer, and that seems to do it.
With qprd and mblmin=1
Video stream: 7640.677 kbit/s
PSNR: Y:49.86, Cb:50.15, Cr:50.71, All:50.04
Bitrate (and PSNR) are approximately the same as without qprd. On such a
short video, I would expect at least that much variation.
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