[x264-devel] Multislicing support

[Etienne Bömcke]

Ok, I just finished a batch of tests, and here are my conclusions :

1. Comparison of x264's fdec.yuv and JM output show no difference,  
regardless of the size of the sequence and the parameters used (both -- 
mb-slicesize and --max-slicesize).

2. When forcing a large number of slice ( more than 4 showed my  
tests ), the decoder isn't able to perform. It fails with the message  
"free_mem2Dpel: trying to free unused memory", which leads me to  
believe that the error is in the decoder code. I suppose the program  
cannot handle the decoding of many slices, as x264 behaves perfectly  
well during the encoding.
I just tried reading an output stream with more than 4 slices with  
VLC, and although the stream is read without VLC giving an error, the  
image appears only in the last seconds. I'll have to investigate this  
problem further and check if the error lies in the patched code.

3. Encoding speed is reduced by up to 10% when using the patched code  
to encode in one slice.

4. Output stream bitrate increases significantly regardless of which  
bitrate control method is used (fixed Q or target bitrate).

The last two observations indicate that there's something messing the  
rate control in the patch. I did more tests with the patch only  
partially applied, and I think the problem comes from the modification  
of the stats computation. I did not write this code myself, it was  
Mojtaba who did. Mojtaba, could you give it a look and check if  
there's no mistake in the stats computation?

I'll try to resolve the problem of the many slices, if I manage  
interesting results I'll let you know.

Thank you all for your feedback,

Etienne


On 23 Apr 2008, at 16:17, Mojtaba Hosseini wrote:

>> -----Original Message-----
>> From: x264-devel-bounces at videolan.org on behalf of List, Peter
>> Sent: Wed 4/23/2008 9:17 AM
>> To: x264-devel at videolan.org
>> Subject: Re: [x264-devel] Multislicing support
>> Hallo Etienne,
>> I would appreciate very much if this patch would go into the
>> official version.
>> One more question: In your last mail you explicitly mentioned
>> the option where a slice is "slicesize" macroblocks big.
>> If I remember rightly Mojtaba Hosseini promoted the version
>> of restricting a slice by the number of bytes it has. Is that
>> also part of your patch? In you conversation with Mojtaba
>> Hosseini in Feb. 2008 this seemed to be the case...
>> Regards
>> Peter
>
> I just confirmed that the patch works for me as well. That is,
> the slice size threshold (by bytes) is included in Etienne's patch.
> I would also really appreciate having this patch make it into the
> repository. Anyone else using this patch?
>
> Mojtaba Hosseini
> <winmail.dat>_______________________________________________
> x264-devel mailing list
> x264-devel at videolan.org
> http://mailman.videolan.org/listinfo/x264-devel

--
Etienne Bömcke
UCL - Laboratoire TELE
etienne.bomcke at uclouvain.be