[x264-devel] Re: tiles

[reamer-s at Safe-mail.net]

-------- Original Message --------
From: Loren Merritt <lorenm at u.washington.edu>

> >> The concept of encoding in slices and stitching together a final bitstream 
> >> is quiet frequently used in cases where a multiprocessor system is 
> >> available to improve encoding speeds. The H264 standard itself supports the 
> >> slice encoding feature very well. This approach will work with other AVC 
> >> like formats if slice level encoding is supported.
> 
> Just note that slice-groups (needed for any shape other than raster scan) 
> are allowed only in baseline and extended profiles.

My application is for encoding HD up to 1080i.  What is the impact of these profile restrictions?

> 
> > ASP supports it even better as no in-loop filter is involved and thus 
> > multi-slice encoding can be completely transparent.
> 
> Multislice, yes. But can ASP do non-raster-shaped slices? Or would you 
> put each scanline of each region into its own slice?
> 
> And no matter what, you'll still lose some quality because inter blocks 
> can't predict MVs from across the slice border.

If the tiles each cover a relatively large portion of the frame does that help?

> 
> > It's even not neccessary to lose quality when all threads have the complete 
> > reference frames at their disposal :)
> 
> You would lose a whole lot of quality if each thread did not have access 
> to the complete reference frame, since you'd have to avoid any motion 
> compensation that involves pixels from other slices. And that's not just 
> MVs that span the slice border, but also MVs within the slice that point 
> within a few pixels of the border (due to 6tap (H.264) or 8tap (ASP qpel) 
> subpel interpolation).

hmmmm... 

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