[FFmpeg-devel] [PATCH v2 1/2] libavformat/mpegts: Extract arib_caption descriptor data into codecpar->extradata

[magic xqq]

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.


On Sun, Apr 11, 2021 at 7:41 PM Marton Balint <cus at passwd.hu> wrote:
>
>
>
> On Sat, 10 Apr 2021, zheng qian wrote:
>
> > Changes since v1:
> >  If desc_len < 3, break the switch statement instead of return AVERROR_INVALIDDATA
> >  to make it more robust.
> >  For arib_caption, data_component_descriptor should contains at least 3 bytes:
> >  data_component_id: uint16, additional_arib_caption_info: uint8.
> >
> > The recognization of ARIB STD-B24 caption has been introduced in commit a03885b,
> > which is used as closed caption in Japanese / Brazilian Digital Television.
> >
> > But whenever copying arib_caption into mpegts output, arib_caption inside the
> > outputted stream cannot be recgonized as a arib_caption subtitle track once again,
> > which is caused by the missing of descriptors in the PMT table.
> >
> > These patches are intended to fix broken stream copying of arib_caption subtitle.
> >
> > This patch extracts necessary fields into codecpar->extradata for future remuxing,
> > which describe the stream_identifier, the profile and other additional information.
> >
> > Signed-off-by: zheng qian <xqq at xqq.im>
> > ---
> > libavformat/mpegts.c | 25 +++++++++++++++++++++++++
> > 1 file changed, 25 insertions(+)
> >
> > diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
> > index 6e0d9d7496..fd7ea1f504 100644
> > --- a/libavformat/mpegts.c
> > +++ b/libavformat/mpegts.c
> > @@ -2107,6 +2107,9 @@ int ff_parse_mpeg2_descriptor(AVFormatContext *fc, AVStream *st, int stream_type
> >         // STD-B24, fascicle 3, chapter 4 defines private_stream_1
> >         // for captions
> >         if (stream_type == STREAM_TYPE_PRIVATE_DATA) {
> > +            if (desc_len < 3)
> > +                break;
> > +
> >             // This structure is defined in STD-B10, part 1, listing 5.4 and
> >             // part 2, 6.2.20).
> >             // Listing of data_component_ids is in STD-B10, part 2, Annex J.
> > @@ -2145,6 +2148,28 @@ int ff_parse_mpeg2_descriptor(AVFormatContext *fc, AVStream *st, int stream_type
> >             st->codecpar->codec_id   = AV_CODEC_ID_ARIB_CAPTION;
> >             st->codecpar->profile    = picked_profile;
> >             st->internal->request_probe        = 0;
> > +
> > +            // Store stream_identifier and payload of data_component_descriptor
> > +            // (data_component_id & additional_arib_caption_info) as extradata.
> > +            // data_component_descriptor is defined in ARIB STD-B10, part 2, 6.2.20
> > +            // These will be useful for remuxing arib_caption into mpegts output.
> > +            if (!st->codecpar->extradata) {
> > +                st->codecpar->extradata = av_mallocz(4 + AV_INPUT_BUFFER_PADDING_SIZE);
> > +                if (!st->codecpar->extradata)
> > +                    return AVERROR(ENOMEM);
> > +
> > +                st->codecpar->extradata_size = 4;
> > +
> > +                // stream_identifier (component_tag of stream_identifier_descriptor)
> > +                st->codecpar->extradata[0] = (uint8_t)(st->stream_identifier - 1);
>
> Storing this in extradata seems redundant. AVStream->stream_identifier
> already exists, and you should be able to use that for muxing as well.
>
> Regards,
> Marton
>
> > +
> > +                // payload of data_component_descriptor structure
> > +                // data_component_id
> > +                st->codecpar->extradata[1] = (uint8_t)((data_component_id & 0xF0) >> 8);
> > +                st->codecpar->extradata[2] = (uint8_t)(data_component_id & 0x0F);
> > +                // additional_arib_caption_info, defined in ARIB STD-B24, fascicle 1, Part 3, 9.6.1
> > +                st->codecpar->extradata[3] = get8(pp, desc_end);
> > +            }
> >         }
> >         break;
> >     case 0xb0: /* DOVI video stream descriptor */
> > --
> > 2.29.2
> >
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