[FFmpeg-devel] [RFC] encoder profile validation

[Marton Balint]

Hi,

As you may know, a recent patchset enabled AVCodecContext->profile 
constants to reside in encoders.

In order to make a full transition to avctx->profile even in existing 
encoders which might use a private profile setting, we have to make sure 
only supported avctx->profile values are passed to encoders.

The fact that avctx->profile is not validated is already an issue, and 
assertions/segmentation faults can already happen in existing encoders 
(e.g.: aac, mpeg) if unsupported values are passed.

AVCodec have a .profiles attribute which supposed to contain the list of 
supported profiles. However this is problematic because
- AVCodecContext->profile is not validated against this list
- not all encoders define the list
- even if there is a list it might be defined as NULL_IF_CONFIG_SMALL
- some encoders support more or less than its currently defined list
- AVCodec->profiles contains AVProfiles which supposed to have a textual
   representation of each profile, which can cause profile name
   duplications/inconsistencies against libavcodec/profiles.c if the list
   is different to the one in codecs profile list.

So I'd rather not user AVCodec->profiles for this validation. I am 
thinking about two possible solutions:

1) Add a new AVCodec->supported_profiles attribute which is a simple 
integer list and validate against this list

or

2) Introdce a new OPT type, AV_OPT_TYPE_ENUM which validates against the 
values of its named constants. This has the benefit that the supported 
profiles only appear once in the AVClass option list, but it also 
means that encoders might not share the supported profiles list via a 
#define in libavcodec/profile.h, because they might support different 
profiles.

I like the second approach better, but let me know what you think.

Thanks,
Marton