[FFmpeg-devel] [PATCH 2/6] vaapi: Remove H.264 baseline profile

Li, Zhong zhong.li at intel.com
Wed Oct 11 11:10:52 EEST 2017

> -----Original Message-----
> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> Of Mark Thompson
> Sent: Tuesday, October 10, 2017 6:36 AM
> To: ffmpeg-devel at ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH 2/6] vaapi: Remove H.264 baseline
> profile
> On 09/10/17 22:48, Carl Eugen Hoyos wrote:
> > 2017-10-09 13:21 GMT+02:00 wm4 <nfxjfg at googlemail.com>:
> >
> >> Shouldn't trying to decode baseline video just fall back to sw decoding?
> >
> > Given that software doesn't support the specific features of baseline
> > either, I don't think this helps.
> > I was under the impression the only sane thing to do when reading
> > baseline H.264 is printing a warning and continue as if constraint
> > baseline was detected.
> At least with software decode we would know that it has failed - an
> inconvenient property of many hardware decoders is their reluctance to
> report errors usefully or at all.
> Hence the warning on using the ALLOW_PROFILE_MISMATCH flag, which
> does allow the attempt to decode baseline profile streams with hardware:
> """
> If the stream is actually not supported then the behaviour is undefined, and
> may include returning entirely incorrect output while indicating success.
> """
> I think the behaviour we have now with this option to continue if the user
> really wants (and is aware of the possible consequences) is correct.

[Li, Zhong] There advanced features of baseline profile are not supported´╝ÜFMO, SAO, and Redundant slices. 
So another way is to check a baseline clip has some of these there features or not (ie, slice_group_number can be check when decoding PPS),
If yes, fall back to sw decoding. Else, set the profile to be constrained profile. 

> Thanks,
> - Mark
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