[FFmpeg-devel] MAX_SLICES in H.264 / Also, FMO

Jason Garrett-Glaser darkshikari
Wed Jun 9 17:56:12 CEST 2010

On Wed, Jun 9, 2010 at 7:15 AM, Mike Melanson <mike at multimedia.cx> wrote:
> I tried to process a raw H.264 file that complained about the max slices
> being exceeded and that I should increase MAX_SLICES and the program should
> be recompiled. Sure enough, changing MAX_SLICES from 16 -> 32 fixed the
> problem. What does the standard say about how many slices a decoder must
> support?

Nothing, particularly.  Note that with actual slices > 16, nothing
actually breaks unless the slices use different reference frame orders
in deblock, which they never do.  Do note, however, that this is only
true for ffh264: for DXVA, slices > MAX_SLICES will cause instant

> Further, I have some more streams that can't be processed because something
> called FMO is reportedly not implemented. Looking at the code (h264_ps.c), I
> get the impression that no FMO files have ever been encountered in the wild,
> so the support was never enabled and debugged. Is that true?

I recall Michael giving a quote around $10k for implementation of FMO.
 It's a useless feature that nobody cares about and is complicated.

Dark Shikari

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