h264parse: parse unregistered SEI without user data

We get loads of warnings when parsing videos from users:

gsth264parser.c:1115:gst_h264_parser_parse_user_data_unregistered: No more remaining payload data to store
gsth264parse.c:646:gst_h264_parse_process_sei:<h264parse0> failed to parse one or more SEI message

Those are raised because of unregistered SEI without user data.

The spec does not explicitly state that unregistered SEI needs to have
data and I suppose the UUID by itself can carry valuable information.
FFmpeg also parses and exposes such SEI so there is no reason for us no
too as well.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7931>

girs/GstVideo-1.0.gir

@@ -16746,7 +16746,7 @@ parameters.</doc>
           <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/video/video-sei.c">User Data Unregistered UUID</doc>
           <type name="guint8" c:type="guint8*"/>
         </parameter>
-        <parameter name="data" transfer-ownership="none">
+        <parameter name="data" transfer-ownership="none" nullable="1" allow-none="1">
           <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/video/video-sei.c">SEI User Data Unregistered buffer</doc>
           <type name="guint8" c:type="guint8*"/>
         </parameter>

subprojects/gst-plugins-bad/gst-libs/gst/codecparsers/gsth264parser.c

@@ -1111,12 +1111,6 @@ gst_h264_parser_parse_user_data_unregistered (GstH264NalParser * nalparser,
     READ_UINT8 (nr, data[i], 8);
   }
 
-  if (payload_size < 1) {
-    GST_WARNING ("No more remaining payload data to store");
-    g_clear_pointer (&data, g_free);
-    return GST_H264_PARSER_BROKEN_DATA;
-  }
-
   urud->data = data;
   GST_MEMDUMP ("SEI user data unregistered", data, payload_size);
   return GST_H264_PARSER_OK;

subprojects/gst-plugins-bad/gst/videoparsers/gsth264parse.c

@@ -623,9 +623,6 @@ gst_h264_parse_process_sei_user_data_unregistered (GstH264Parse * h264parse,
 {
   GstByteReader br;
 
-  if (urud->data == NULL || urud->size < 1)
-    return;
-
   gst_byte_reader_init (&br, urud->data, urud->size);
 
   gst_video_parse_user_data_unregistered ((GstElement *) h264parse,

subprojects/gst-plugins-bad/tests/check/elements/h264parse.c

@@ -1488,6 +1488,16 @@ GST_START_TEST (test_parse_sei_userdefinedunregistered)
     0x1f, 0x00, 0x05, 0xff, 0x21, 0x7e, 0xff, 0x29,
     0xb5, 0xff, 0xdc, 0x13
   };
+  // Same SEI as above but without data
+  const guint8 no_data_sei[] = {
+    0x00, 0x00, 0x00, 0x20, 0x06, 0x05, 0x10, 0x4d,
+    0x49, 0x53, 0x50, 0x6d, 0x69, 0x63, 0x72, 0x6f,
+    0x73, 0x65, 0x63, 0x74, 0x69, 0x6d, 0x65,
+    /* IDR frame (doesn't match caps) */
+    0x00, 0x00, 0x00, 0x14, 0x65, 0x88, 0x84, 0x00,
+    0x10, 0xff, 0xfe, 0xf6, 0xf0, 0xfe, 0x05, 0x36,
+    0x56, 0x04, 0x50, 0x96, 0x7b, 0x3f, 0x53, 0xe1
+  };
 
   h = gst_harness_new ("h264parse");
 
@@ -1511,6 +1521,21 @@ GST_START_TEST (test_parse_sei_userdefinedunregistered)
 
   gst_buffer_unref (buf);
 
+  // Now try parsing an unregistered SEI without data
+  buf = gst_buffer_new_and_alloc (misb_sei_size);
+  gst_buffer_fill (buf, 0, no_data_sei, sizeof (no_data_sei));
+  fail_unless_equals_int (gst_harness_push (h, buf), GST_FLOW_OK);
+
+  buf = gst_harness_pull (h);
+  meta = gst_buffer_get_video_sei_user_data_unregistered_meta (buf);
+  fail_unless (meta != NULL);
+
+  fail_unless (memcmp (meta->uuid, H264_MISP_MICROSECTIME, 16) == 0);
+  fail_unless (meta->data == NULL);
+  fail_unless (meta->size == 0);
+
+  gst_buffer_unref (buf);
+
   gst_harness_teardown (h);
 }
 

subprojects/gst-plugins-base/gst-libs/gst/video/video-sei.c

@@ -156,7 +156,7 @@ gst_video_sei_user_data_unregistered_meta_get_info (void)
  * gst_buffer_add_video_sei_user_data_unregistered_meta:
  * @buffer: a #GstBuffer
  * @uuid: User Data Unregistered UUID
- * @data: (transfer none): SEI User Data Unregistered buffer
+ * @data: (transfer none) (allow-none): SEI User Data Unregistered buffer
  * @size: size of the data buffer
  *
  * Attaches #GstVideoSEIUserDataUnregisteredMeta metadata to @buffer with the given
@@ -172,7 +172,6 @@ gst_buffer_add_video_sei_user_data_unregistered_meta (GstBuffer * buffer,
 {
   GstVideoSEIUserDataUnregisteredMeta *meta;
   g_return_val_if_fail (GST_IS_BUFFER (buffer), NULL);
-  g_return_val_if_fail (data != NULL, NULL);
 
   meta = (GstVideoSEIUserDataUnregisteredMeta *) gst_buffer_add_meta (buffer,
       GST_VIDEO_SEI_USER_DATA_UNREGISTERED_META_INFO, NULL);