cccombiner: fix output-padding=false for a cea608 field 1 only stream

If we have data that needs outputting but we have to output padding to
meet the alternating field requirements of cea608, then output that
padding anyway.

Also includes a test

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4124>

subprojects/gst-plugins-bad/ext/closedcaption/ccutils.c

@@ -775,10 +775,17 @@ cc_buffer_get_out_sizes (CCBuffer * buf, const struct cdp_fps_entry *fps_entry,
     wrote_first = TRUE;
   }
 
+  // don't write padding if not requested
   if (!buf->output_padding && write_cea608_1_size == 0
       && write_cea608_2_size == 0) {
-    *field1_padding = 0;
+    // however if we are producing data for a cdp that only has a single 608 field,
-    *field2_padding = 0;
+    // in order to keep processing data will still need to alternate fields and
+    // produce the relevant padding data
+    if (fps_entry->max_cea608_count != 1 || (extra_cea608_1 == 0
+            && extra_cea608_2 == 0)) {
+      *field1_padding = 0;
+      *field2_padding = 0;
+    }
   }
 
   GST_TRACE_OBJECT (buf, "allocated sizes ccp:%u, cea608-1:%u (pad:%u), "

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

@@ -29,6 +29,8 @@
 #include <string.h>
 
 static GstStaticCaps foo_bar_caps = GST_STATIC_CAPS ("foo/bar");
+static GstStaticCaps foo_bar_caps_60fps =
+GST_STATIC_CAPS ("foo/bar,framerate=60/1");
 static GstStaticCaps cea708_cc_data_caps =
 GST_STATIC_CAPS ("closedcaption/x-cea-708,format=(string) cc_data");
 
@@ -191,6 +193,106 @@ GST_START_TEST (captions_and_eos)
 
 GST_END_TEST;
 
+GST_START_TEST (captions_no_output_padding_60fps_608_field1_only)
+{
+  GstHarness *h, *h2;
+  GstBuffer *outbuf;
+  GstPad *caption_pad;
+  GstCaps *caps;
+  GstVideoCaptionMeta *meta;
+  const guint8 cc_data[3] = { 0xfc, 0x20, 0x20 };
+  int i = 0;
+
+  h = gst_harness_new_with_padnames ("cccombiner", "sink", "src");
+  h2 = gst_harness_new_with_element (h->element, NULL, NULL);
+  caption_pad = gst_element_request_pad_simple (h->element, "caption");
+  gst_harness_add_element_sink_pad (h2, caption_pad);
+  gst_object_unref (caption_pad);
+
+  g_object_set (h->element, "emit-signals", TRUE, NULL);
+  g_signal_connect (h->element, "samples-selected",
+      G_CALLBACK (samples_selected_cb), NULL);
+  g_object_set (h->element, "output-padding", FALSE, NULL);
+
+  gst_element_set_state (h->element, GST_STATE_NULL);
+  gst_element_set_state (h->element, GST_STATE_PLAYING);
+
+  gst_harness_set_src_caps_str (h, foo_bar_caps_60fps.string);
+  gst_harness_set_src_caps_str (h2, cea708_cc_data_caps.string);
+
+  /* Push a buffer and caption buffer */
+  for (i = 0; i < 8; i++) {
+    GstBuffer *video_buf, *caption_buf = NULL;
+
+    video_buf = gst_buffer_new_and_alloc (128);
+    GST_BUFFER_PTS (video_buf) = i * 40 * GST_MSECOND;
+    GST_BUFFER_DURATION (video_buf) = 40 * GST_MSECOND;
+    gst_harness_push (h, video_buf);
+
+    caption_buf = gst_buffer_new_and_alloc (3);
+    gst_buffer_fill (caption_buf, 0, cc_data, 3);
+    GST_BUFFER_PTS (caption_buf) = i * 40 * GST_MSECOND;
+    GST_BUFFER_DURATION (caption_buf) = 40 * GST_MSECOND;
+    gst_harness_push (h2, caption_buf);
+
+    /* Pull the previous output buffer */
+    if (i > 0) {
+      int j;
+      outbuf = gst_harness_pull (h);
+      fail_unless (outbuf != NULL);
+
+      meta = gst_buffer_get_video_caption_meta (outbuf);
+      fail_unless (meta != NULL);
+      fail_unless_equals_int (meta->caption_type,
+          GST_VIDEO_CAPTION_TYPE_CEA708_RAW);
+      fail_unless_equals_int (meta->size, 3);
+      GST_MEMDUMP ("caption data", meta->data, meta->size);
+
+      for (j = 0; j < meta->size; j++) {
+        if ((i % 2) == 1) {
+          fail_unless_equals_int (meta->data[j], cc_data[j]);
+        } else {
+          int padding_field2[] = { 0xf9, 0x80, 0x80 };
+          fail_unless_equals_int (meta->data[j], padding_field2[j]);
+        }
+      }
+
+      gst_buffer_unref (outbuf);
+    }
+    expected_video_buffer = video_buf;
+    if (caption_buf)
+      expected_caption_buffer = caption_buf;
+  }
+
+  /* Push EOS on both pads get the second output buffer, we otherwise wait
+   * in case there are further captions for the current video buffer */
+  gst_harness_push_event (h, gst_event_new_eos ());
+  gst_harness_push_event (h2, gst_event_new_eos ());
+
+  outbuf = gst_harness_pull (h);
+  fail_unless (outbuf != NULL);
+
+  meta = gst_buffer_get_video_caption_meta (outbuf);
+  fail_unless (meta != NULL);
+  fail_unless_equals_int (meta->caption_type,
+      GST_VIDEO_CAPTION_TYPE_CEA708_RAW);
+  fail_unless_equals_int (meta->size, 3);
+
+  gst_buffer_unref (outbuf);
+
+  /* Caps should be equal to input caps */
+  caps = gst_pad_get_current_caps (h->sinkpad);
+  fail_unless (caps != NULL);
+  fail_unless (gst_caps_can_intersect (caps,
+          gst_static_caps_get (&foo_bar_caps)));
+  gst_caps_unref (caps);
+
+  gst_harness_teardown (h);
+  gst_harness_teardown (h2);
+}
+
+GST_END_TEST;
+
 static Suite *
 cccombiner_suite (void)
 {
@@ -201,6 +303,7 @@ cccombiner_suite (void)
 
   tcase_add_test (tc, no_captions);
   tcase_add_test (tc, captions_and_eos);
+  tcase_add_test (tc, captions_no_output_padding_60fps_608_field1_only);
 
   return s;
 }