On Sun, Apr 11, 2021 at 4:58 PM Jan Ekström <jee...@gmail.com> wrote:
>
> On Sun, Apr 11, 2021 at 4:25 PM magic xqq <x...@xqq.im> wrote:
> >
> > I have already tried to use st->stream_identifier directly in mpegtsenc.c
> > while handling arib_caption stream in mpegts_write_pmt() function.
> >
> > But in mpegtsenc.c, st->stream_identifier always provides
> > an incorrect value of 0, which should be 0x30 for arib_caption A profile.
> >
> > st->stream_identifier seems hasn't been copied correctly while remuxing into
> > another mpegts stream. So I manually copied it.
> >
>
> Yes, AVStream::stream_identifier is not currently handled by ffmpeg.c.
> Not sure its addition was ever really thought thoroughly, and mostly
> added so that MPEG-TS reading clients could gain this value when
> reading data. Not even ffprobe.c is currently poking a stick at it.
>
> But quickly looking at things, you can map component_tag and
> component_id according to the ARIB caption profile, since your
> possibilities are:
>
> FF_PROFILE_ARIB_PROFILE_A => component tag 0x30-0x37, data_component_id =
> 0x0008
> FF_PROFILE_ARIB_PROFILE_C => component_tag 0x87, data_component_id = 0x0012
>
> The only issue is if you want to keep the exact same component tag,
> but that can be improved in ffmpeg.c by just passing it during stream
> copy into the output AVStream if it's nonzero (that is why it's
> identifier plus 1). Also probably we need an option to force it to
> something else if needed. In any case, I consider this somewhat
> separate from the remux case since I don't think you need to have the
> exact same id for the remux to be workable? Please note if I am
> mistaken.
>
> Then there's the extra info, I'll have to check the specs later today
> whether that contains anything dynamic.
>
> Best regards,
> Jan
Alright, so that additional data structure is one byte large and
contains the following things:
additional_arib_caption_info(){
DMF bslbf(4)
Reserved bslbf(2)
Timing bslbf(2)
}
DMF - (Display mode flag), with b1111 being the most common value "dynamic"
Timing - async|program sync|real time sync
So I guess at the very least this would make sense to add into the
extradata. I do find it interesting though that libaribb24 doesn't
seem to require this data for valid decoding at all :D (although I
guess mostly the output timing and automated subtitle sub-stream
selection is affected by these values).
Jan
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
