[x264-devel] Boundary constraints

[Etienne Bömcke]

Thanks a lot for your advises. I'll send you a feedback about the  
different methods if I achieve interesting results.

On 24 Nov 2007, at 10:08, Loren Merritt wrote:

> On Wed, 21 Nov 2007, Etienne Bömcke wrote:
>
>>> Do your banners go only on the bottom of the frame, or would you
>>> ever want to replace e.g. the left side? Your example is
>>> inconsistent: 200x576 would be a side.
>>
>> You're right about the dimensions, it was a mistake. I meant  
>> something
>> like 720x150. As for now I only need bottom banners, but if there's a
>> way to do this with any part of the sequence that would be way  
>> better.
>>
>>> This is important bause you really don't want to implement it
>>> without slices, and slices normally only stack vertically.
>>
>> I'm afraid I don't really understand this... I thought about using
>> slices, but as x264 currently doesn't support slices I was wondering
>> if there was another way to achieve that goal. When you say slices
>> only stack vertically, are you talking about that patch of yours you
>> were mentioning in a former mail?
>
> The following pertains to what is possible within the H.264  
> standard, not any specific implementation. I don't foresee a patch  
> for any of these methods being clean enough nor useful enough to  
> accept in x264, but that doesn't stop you from implementing it on  
> your own.
>
> In every case, I will talk only about appending videos. If you also  
> want the original frame without any overlays, then just treat the  
> overlayed piece of the original frame as another potential video to  
> be appended.
>
> Method 1, for vertically stacked videos only:
> Make sure the top video uses no motion vectors off the bottom, nor  
> subpel motion vectors within 3 pixels of the bottom (because subpel  
> interpolation would involve pixels off the bottom), and likewise for  
> the top edge of the bottom video. Make sure all the videos use the  
> same frame types. Then concatenate pairs of frames, adjust first_mb  
> of the bottom slice, disable deblocking across slice boundaries, and  
> you have one multisliced video. No bitstream rewriting is necessary  
> outside the headers.
>
> Method 2, for any arrangement of videos:
> Code the individual videos with the same motion constraints as (1).  
> When concatenating frames, add slice groups to specify shapes other  
> than a vertical stack. Slice groups require Extended profile, which  
> is incompatible with cabac, 8x8dct, cqm, and a few other features.
>
> Method 3, for any arrangement of videos:
> Code the individual videos with the same motion constraints as (1).  
> Additionally, the top-left macroblock in all intra frames in the  
> video(s) to be placed on the bottom/right must be coded with a  
> sufficiently low QP that its DC coefficient is lossless. The top- 
> left macroblock in non-intra frames must be either similarly  
> lossless or not intra. All other intra blocks on the edge must use  
> vertical or horizontal prediction (depending on which edge it is),  
> not DC prediction. Either don't use deblocking at all, or make the  
> macroblocks along the edge sufficiently low QP that they don't get  
> deblocked. If all of those constraints are satisfied, then you can  
> rewrite the bitstream to merge the videos without slices.
>
> Method 4, for any arrangement of videos:
> Use switching pictures. But these also require Extended profile, and  
> slice groups are better for your purpose.
>
> --Loren Merritt_______________________________________________
> 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