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

[Corey Hickey]

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
>> 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

Do you mean mbqmin? mblmin doesn't seem to exist, though I haven't 
looked at the source yet.

No change with mbqmin=1.

-Corey