[FFmpeg-devel] [PATCH v4 8/9] lavc/libopenh264enc: allow specifying the profile through AVCodecContext

[Fu, Linjie]

> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Martin Storsjö
> Sent: Tuesday, April 28, 2020 04:13
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Cc: Fu, Linjie <linjie.fu at intel.com>
> Subject: Re: [FFmpeg-devel] [PATCH v4 8/9] lavc/libopenh264enc: allow
> specifying the profile through AVCodecContext
> 
> On Wed, 15 Apr 2020, Linjie Fu wrote:
> 
> > Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> > ---
> > libavcodec/libopenh264enc.c | 16 ++++++++++++++++
> > 1 file changed, 16 insertions(+)
> >
> > diff --git a/libavcodec/libopenh264enc.c b/libavcodec/libopenh264enc.c
> > index 0fe8cf4..4d337d2 100644
> > --- a/libavcodec/libopenh264enc.c
> > +++ b/libavcodec/libopenh264enc.c
> > @@ -113,6 +113,22 @@ static av_cold int
> svc_encode_init_profile(AVCodecContext *avctx, SEncParamExt *
> > {
> >     SVCContext *s = avctx->priv_data;
> >
> > +    /* Allow specifying the libopenh264 profile through AVCodecContext.
> */
> > +    if (FF_PROFILE_UNKNOWN == s->profile &&
> > +        FF_PROFILE_UNKNOWN != avctx->profile)
> > +        switch (avctx->profile) {
> > +        case FF_PROFILE_H264_CONSTRAINED_BASELINE:
> > +            s->profile = FF_PROFILE_H264_CONSTRAINED_BASELINE;
> > +            break;
> > +        case FF_PROFILE_H264_HIGH:
> > +            s->profile = FF_PROFILE_H264_HIGH;
> > +            break;
> > +        default:
> > +            av_log(avctx, AV_LOG_WARNING,
> > +                   "Unsupported avctx->profile: %d.\n", avctx->profile);
> > +            break;
> > +        }
> > +
> >     if (s->profile == FF_PROFILE_UNKNOWN)
> >         s->profile = s->cabac ? FF_PROFILE_H264_HIGH :
> >                                 FF_PROFILE_H264_CONSTRAINED_BASELINE;
> 
> With this in place, why even do the previous commit, why not just go for
> only using avctx->profile? Although as far as I can see, that field
> doesn't seem to have string options for sepcifying H264 profiles, so it
> can only be set via code or by specifying a numberic value - is that
> right?

Yes, code/numberic value works in this way, however maybe not straight
forward enough for user.

> Wouldn't it just be best to add the H264 profiles to options_table.h to
> keep allowing it to be set via a string, but remove the internal
> s->profile field here, as patch 7/9 already breaks handling of the profile
> field by stopping recognizing "main" and only recognizing "high" anyway.

Most sw codecs like libx264/libx265 and hw codecs like h264_vaapi/h264_nvenc
have the logic of :
1. derive the settings from avctx->profile which is determined in options_table.h;
2. If not, check the private option for specific encoder;

And specifically for libopenh264enc,  we allow one more logic:
3. determine the profile by s->cabac;

I admit it'll be good if settled this down to parse all possible profiles for each codec
(maybe according to libavcodec/profiles.c), hence we may remove similar/redundant
logics in specific encoder(x264/h264_vaapi/h264_nvenc).

Please help to comment whether it makes sense for you all, since this would impact
many codecs.

- Linjie