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

[zheng qian]

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);
+
+                // 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