[FFmpeg-devel] [PATCH 3/5] mpegts: add channel specific languages into metadata

[Janne Grunau]

On Mon, Feb 14, 2011 at 11:11:45PM +0000, M?ns Rullg?rd wrote:
> > +                if (!language_key)
> > +                    break;
> > +                language_key[7] = '0' + ch;
> > +                language[0] = combined_lang[ch * 4 + 0] = get8(pp, desc_end);
> > +                language[1] = combined_lang[ch * 4 + 1] = get8(pp, desc_end);
> > +                language[2] = combined_lang[ch * 4 + 2] = get8(pp, desc_end);
> > +                language[3] = 0;
> > +                combined_lang[ch * 4 + 3] = '+';
> > +                av_metadata_set2(&st->metadata, language_key, language,
> > +                                 AV_METADATA_DONT_STRDUP_KEY);
> > +                if (get8(pp, desc_end))
> > +                    av_log_ask_for_sample(fc, "Multiple languages and non-zero audio_type.");
> > +            }
> > +            combined_lang[tag_count * 4 - 1] = 0;
> > +            av_metadata_set2(&st->metadata, "language", combined_lang,
> > +                             AV_METADATA_DONT_STRDUP_VAL);
> 
> I don't understand the idea behind this.  The descriptor applies to one
> program element (AVStream).  If it contains several language codes, this
> simply means the stream contains multiple languages.  The MPEG spec
> doesn't specify any further interpretation.  Does DVB use this to
> indicate multiple mono streams coded as one elementary stream?  I don't
> have those specs at hand.

The component descriptor is afaik the only way to signal dual mono mpeg
layer 2 streams for DVB. It doesn't specify how multiple languages in
the ISO 639 language descriptor should be interpreted. Dual mono is
generally considered deprecated in DVB.

Janne