From d471be4f3ad370deceeecedc7cfe9daba73bc528 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Thu, 20 Dec 2018 11:31:58 +0200
Subject: [PATCH] qtdemux: Extract CEA608 framerate from the (first) video
 stream

EA608 closed caption tracks are a bit special in that each sample
can contain CCs for multiple frames, and CCs can be omitted and have to
be inferred from the duration of the sample then.

As such we take the framerate from the (first) video track here for
CEA608 as there must be one CC byte pair for every video frame
according to the spec.

For CEA708 all is fine and there is one sample per frame.
---
 gst/isomp4/qtdemux.c | 54 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 44 insertions(+), 10 deletions(-)

diff --git a/gst/isomp4/qtdemux.c b/gst/isomp4/qtdemux.c
index 2db46d64d8..95e27fdef2 100644
--- a/gst/isomp4/qtdemux.c
+++ b/gst/isomp4/qtdemux.c
@@ -8518,19 +8518,53 @@ gst_qtdemux_configure_stream (GstQTDemux * qtdemux, QtDemuxStream * stream)
     }
   }
 
-  else if (stream->subtype == FOURCC_clcp) {
-    gboolean fps_available = gst_qtdemux_guess_framerate (qtdemux, stream);
+  else if (stream->subtype == FOURCC_clcp && CUR_STREAM (stream)->caps) {
+    const GstStructure *s;
+    QtDemuxStream *fps_stream = NULL;
+    gboolean fps_available = FALSE;
 
-    if (CUR_STREAM (stream)->caps) {
-      CUR_STREAM (stream)->caps =
-          gst_caps_make_writable (CUR_STREAM (stream)->caps);
+    /* CEA608 closed caption tracks are a bit special in that each sample
+     * can contain CCs for multiple frames, and CCs can be omitted and have to
+     * be inferred from the duration of the sample then.
+     *
+     * As such we take the framerate from the (first) video track here for
+     * CEA608 as there must be one CC byte pair for every video frame
+     * according to the spec.
+     *
+     * For CEA708 all is fine and there is one sample per frame.
+     */
 
-      /* set framerate if calculated framerate is reliable */
-      if (fps_available) {
-        gst_caps_set_simple (CUR_STREAM (stream)->caps,
-            "framerate", GST_TYPE_FRACTION, CUR_STREAM (stream)->fps_n,
-            CUR_STREAM (stream)->fps_d, NULL);
+    s = gst_caps_get_structure (CUR_STREAM (stream)->caps, 0);
+    if (gst_structure_has_name (s, "closedcaption/x-cea-608")) {
+      gint i;
+
+      for (i = 0; i < QTDEMUX_N_STREAMS (qtdemux); i++) {
+        QtDemuxStream *tmp = QTDEMUX_NTH_STREAM (qtdemux, i);
+
+        if (tmp->subtype == FOURCC_vide) {
+          fps_stream = tmp;
+          break;
+        }
       }
+
+      if (fps_stream) {
+        fps_available = gst_qtdemux_guess_framerate (qtdemux, fps_stream);
+        CUR_STREAM (stream)->fps_n = CUR_STREAM (fps_stream)->fps_n;
+        CUR_STREAM (stream)->fps_d = CUR_STREAM (fps_stream)->fps_d;
+      }
+    } else {
+      fps_available = gst_qtdemux_guess_framerate (qtdemux, stream);
+      fps_stream = stream;
+    }
+
+    CUR_STREAM (stream)->caps =
+        gst_caps_make_writable (CUR_STREAM (stream)->caps);
+
+    /* set framerate if calculated framerate is reliable */
+    if (fps_available) {
+      gst_caps_set_simple (CUR_STREAM (stream)->caps,
+          "framerate", GST_TYPE_FRACTION, CUR_STREAM (stream)->fps_n,
+          CUR_STREAM (stream)->fps_d, NULL);
     }
   }