gstavviddec: Only allow a single closed caption meta

Following discussion in
https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1396#note_556068

While it is technically possible to store multiple closed caption metas
in the same buffer, we don't currently do that anywhere and for
H264/MPEG2 both parts have to be stored in the same packet, and also the
number of CC bytes you can store per frame is rather limited. This
restriction might be relaxed later once we figured out how to do it
without breaking things.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-libav/-/merge_requests/82>

diff --git a/ext/libav/gstavviddec.c b/ext/libav/gstavviddec.c
index 9f784f4..502390d 100644 (file)
--- a/ext/libav/gstavviddec.c
+++ b/ext/libav/gstavviddec.c
@@ -1691,26 +1691,14 @@ gst_ffmpegviddec_video_frame (GstFFMpegVidDec * ffmpegdec,
     AVFrameSideData *side_data =
         av_frame_get_side_data (ffmpegdec->picture, AV_FRAME_DATA_A53_CC);
     if (side_data) {
-      GstVideoCaptionMeta *cc_meta = NULL;
-      gpointer iter = NULL;
-      gboolean found_708_raw_meta = FALSE;
-
       GST_LOG_OBJECT (ffmpegdec,
           "Found CC side data of type AV_FRAME_DATA_A53_CC, size %d",
           side_data->size);
       GST_MEMDUMP ("A53 CC", side_data->data, side_data->size);
 
-      while ((cc_meta = (GstVideoCaptionMeta *)
-              gst_buffer_iterate_meta_filtered (out_frame->input_buffer, &iter,
-                  GST_VIDEO_CAPTION_META_API_TYPE))) {
-        if (cc_meta->caption_type != GST_VIDEO_CAPTION_TYPE_CEA708_RAW)
-          continue;
-        found_708_raw_meta = TRUE;
-        break;
-      }
-
-      /* do not add CEA 708 caption meta if it already exists */
-      if (!found_708_raw_meta) {
+      /* do not add closed caption meta if it already exists */
+      if (!gst_buffer_get_meta (out_frame->output_buffer,
+              GST_VIDEO_CAPTION_META_API_TYPE)) {
         out_frame->output_buffer =
             gst_buffer_make_writable (out_frame->output_buffer);
         gst_buffer_add_video_caption_meta (out_frame->output_buffer,
@@ -1718,7 +1706,7 @@ gst_ffmpegviddec_video_frame (GstFFMpegVidDec * ffmpegdec,
             side_data->size);
       } else {
         GST_LOG_OBJECT (ffmpegdec,
-            "CEA 708 caption meta already exists: will not add new caption meta");
+            "Closed caption meta already exists: will not add new caption meta");
       }
     }
   }