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

Baptiste Coudurier baptiste.coudurier
Sat Nov 18 17:13:03 CET 2006


Hi

Michael Niedermayer wrote:
> 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.
>>
>> [...]
>>
>> 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
> 

Here I think there is a problem:

sample: test_motion_est.avi on mplayerhq.

ffmpeg -y -i test_motion_est.avi -b 15000k -flags +qprd -flags2 +ivlc
-bf 2 -mbd rd -mblmin 1 -lmin 1 test.m2v

Many frames have q as 4 and some frames bump to 60 for all macroblocks

If you remove -lmin many more frames have 62 as q.

I noticed that if you go CBR:
ffmpeg -y -i test_motion_est.avi -b 15000k -minrate 15000k -maxrate
15000k -bufsize 2300k -flags +qprd -flags2 +ivlc -bf 2 -mbd rd -lmin 1
test.m2v

You experience infinite loop. Increasing bufsize to 2400k solves it
though, but you still have many frames with q as 60.


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