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

[Baptiste Coudurier]

Baptiste Coudurier wrote:
> 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.
> 
> 

Just noticed that removing b frames makes it much more reasonable.
maximum q is around 6. Final bitrate is around 16000k.

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
SMARTJOG S.A.                                    http://www.smartjog.com
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
Phone: +33 1 49966312