[FFmpeg-devel] [PATCH 4/4] vc2enc: only warn on a non-standard base video format

[Rostislav Pehlivanov]

On 17 April 2016 at 03:40, Michael Niedermayer <michael at niedermayer.cc>
wrote:

>
> is this a spec compliance or a profile compliance issue or something
> else ?
>
> from just the Commit message above it sounds a bit like a profile /
> hw decoder limitation, in which case this patch with a different
> av_log() message should be ok ...
>
>
It's a hardware limitation. Basically, SMPTE ST 2042-2:2009 (a separate
specification from the VC-2 specs) defines levels 1-7, an each level has a
few associated base video formats (e.g. 6 for 4K and 3 for 720/1080). So
each hardware decoder which claims to support a level must support all
video formats associated with that level. The VC-2 specifications say
nothing about restricting the level. Our decoder doesn't care about the
level since Dirac was a general purpose codec and so it supports everything.

BTW the encoder hasn't been tested on hardware, and I've only heard of
legends about such existing. The spec isn't well written so I'm pretty sure
turning on huge slice sizes would crash hardware decoders since they'd have
no memory. So the level value doesn't do much at all to ensure hardware can
still decode.