[FFmpeg-devel] [PATCH 1/8] avformat/mpegts: add dvb ac3 descriptor metadata

[lance.lmwang at gmail.com]

On Wed, Jul 22, 2020 at 07:44:06PM +0200, Marton Balint wrote:
> 
> 
> On Wed, 22 Jul 2020, lance.lmwang at gmail.com wrote:
> 
> > From: Limin Wang <lance.lmwang at gmail.com>
> > 
> > Below is one metadata information for the ts with dvb ac3 descriptor audio:
> > ./ffmpeg -i ac3_desc.ts
> >    ...
> >    Stream #0:1[0x294]: Audio: ac3 ([6][0][0][0] / 0x0006), 48000 Hz, 5.1(side), fltp, 448 kb/s
> >    Metadata:
> >      dvb.ac3_desc.component_type: 68
> >      dvb.ac3_desc.bsid: 6
> >      dvb.ac3_desc.mainid: 0
> 
> I don't think it is a good idea to use metadata for this. See how dolby
> vision stores the descripor data, it is using side data and not metadata.
> Also it might make sense to create a generic mpegts descriptor side data
> type?

Thanks for the comments, I'll try to use side data for the descriptor instead. The descriptor is
codec related also, so I have no idea how to make it generic if need to export the field. EAC3
and AC3 may share same type, as it's use reserved bits to extend it. 

> 
> Regards.
> Marton
> 
> > 
> > Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> > ---
> > libavformat/mpegts.c | 22 ++++++++++++++++++++--
> > 1 file changed, 20 insertions(+), 2 deletions(-)
> > 
> > diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
> > index c6fd3e1..1ed7eaf 100644
> > --- a/libavformat/mpegts.c
> > +++ b/libavformat/mpegts.c
> > @@ -2073,15 +2073,33 @@ int ff_parse_mpeg2_descriptor(AVFormatContext *fc, AVStream *st, int stream_type
> >         break;
> >     case 0x6a: /* ac-3_descriptor */
> >         {
> > -            int component_type_flag = get8(pp, desc_end) & (1 << 7);
> > +            uint8_t flags = get8(pp, desc_end);
> > +            uint8_t component_type_flag = flags & (1 << 7);
> > +            uint8_t bsid_flag           = flags & (1 << 6);
> > +            uint8_t mainid_flag         = flags & (1 << 5);
> > +            uint8_t asvc_flag           = flags & (1 << 4);
> > +
> >             if (component_type_flag) {
> > -                int component_type = get8(pp, desc_end);
> > +                uint8_t component_type = get8(pp, desc_end);
> >                 int service_type_mask = 0x38;  // 0b00111000
> >                 int service_type = ((component_type & service_type_mask) >> 3);
> >                 if (service_type == 0x02 /* 0b010 */) {
> >                     st->disposition |= AV_DISPOSITION_DESCRIPTIONS;
> >                     av_log(ts ? ts->stream : fc, AV_LOG_DEBUG, "New track disposition for id %u: %u\n", st->id, st->disposition);
> >                 }
> > +                av_dict_set_int(&st->metadata, "dvb.ac3_desc.component_type", component_type, 0);
> > +            }
> > +            if (bsid_flag) {
> > +                uint8_t bsid = get8(pp, desc_end);
> > +                av_dict_set_int(&st->metadata, "dvb.ac3_desc.bsid", bsid, 0);
> > +            }
> > +            if (mainid_flag) {
> > +                uint8_t mainid = get8(pp, desc_end);
> > +                av_dict_set_int(&st->metadata, "dvb.ac3_desc.mainid", mainid, 0);
> > +            }
> > +            if (asvc_flag) {
> > +                uint8_t asvc = get8(pp, desc_end);
> > +                av_dict_set_int(&st->metadata, "dvb.ac3_desc.asvc", asvc, 0);
> >             }
> >         }
> >         break;
> > -- 
> > 1.8.3.1
> > 
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-- 
Thanks,
Limin Wang