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

[Marton Balint]

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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