line21dec: expose mode property

That new property can be used to control whether and how
detected CC meta should be inserted in the list of existing
CC meta on the input frame (if there was any).

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1885>

2 files changed, 90 insertions, 1 deletions

diff --git a/ext/closedcaption/gstline21dec.c b/ext/closedcaption/gstline21dec.c
index 88a06ed27..489bd0098 100644
--- a/ext/closedcaption/gstline21dec.c
+++ b/ext/closedcaption/gstline21dec.c
@@ -37,13 +37,24 @@
 GST_DEBUG_CATEGORY_STATIC (gst_line_21_decoder_debug);
 #define GST_CAT_DEFAULT gst_line_21_decoder_debug
 
+/**
+ * GstLine21DecoderMode:
+ * @GST_LINE_21_DECODER_MODE_ADD: add new CC meta on top of other CC meta, if any
+ * @GST_LINE_21_DECODER_MODE_DROP: ignore CC if a CC meta was already present
+ * @GST_LINE_21_DECODER_MODE_REPLACE: replace existing CC meta
+ *
+ * Since: 1.20
+ */
+
 enum
 {
   PROP_0,
   PROP_NTSC_ONLY,
+  PROP_MODE,
 };
 
 #define DEFAULT_NTSC_ONLY FALSE
+#define DEFAULT_MODE GST_LINE_21_DECODER_MODE_ADD
 
 #define CAPS "video/x-raw, format={ I420, YUY2, YVYU, UYVY, VYUY, v210 }, interlace-mode=interleaved"
 
@@ -62,6 +73,33 @@ G_DEFINE_TYPE (GstLine21Decoder, gst_line_21_decoder, GST_TYPE_VIDEO_FILTER);
 GST_ELEMENT_REGISTER_DEFINE (line21decoder, "line21decoder",
     GST_RANK_NONE, GST_TYPE_LINE21DECODER);
 
+#define GST_TYPE_LINE_21_DECODER_MODE (gst_line_21_decoder_mode_get_type())
+static GType
+gst_line_21_decoder_mode_get_type (void)
+{
+  static const GEnumValue values[] = {
+    {GST_LINE_21_DECODER_MODE_ADD,
+        "add new CC meta on top of other CC meta, if any", "add"},
+    {GST_LINE_21_DECODER_MODE_DROP,
+          "ignore CC if a CC meta was already present",
+        "drop"},
+    {GST_LINE_21_DECODER_MODE_REPLACE,
+        "replace existing CC meta", "replace"},
+    {0, NULL, NULL}
+  };
+  static volatile GType id = 0;
+
+  if (g_once_init_enter ((gsize *) & id)) {
+    GType _id;
+
+    _id = g_enum_register_static ("GstLine21DecoderMode", values);
+
+    g_once_init_leave ((gsize *) & id, _id);
+  }
+
+  return id;
+}
+
 static void gst_line_21_decoder_finalize (GObject * self);
 static gboolean gst_line_21_decoder_stop (GstBaseTransform * btrans);
 static gboolean gst_line_21_decoder_set_info (GstVideoFilter * filter,
@@ -79,6 +117,9 @@ gst_line_21_decoder_set_property (GObject * object, guint prop_id,
   GstLine21Decoder *enc = GST_LINE21DECODER (object);
 
   switch (prop_id) {
+    case PROP_MODE:
+      enc->mode = g_value_get_enum (value);
+      break;
     case PROP_NTSC_ONLY:
       enc->ntsc_only = g_value_get_boolean (value);
       break;
@@ -95,6 +136,9 @@ gst_line_21_decoder_get_property (GObject * object, guint prop_id,
   GstLine21Decoder *enc = GST_LINE21DECODER (object);
 
   switch (prop_id) {
+    case PROP_MODE:
+      g_value_set_enum (value, enc->mode);
+      break;
     case PROP_NTSC_ONLY:
       g_value_set_boolean (value, enc->ntsc_only);
       break;
@@ -137,6 +181,22 @@ gst_line_21_decoder_class_init (GstLine21DecoderClass * klass)
           "input resolution matches NTSC", DEFAULT_NTSC_ONLY,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GstLine21Decoder:mode
+   *
+   * Control whether and how detected CC meta should be inserted
+   * in the list of existing CC meta on a frame (if any).
+   *
+   * Since: 1.20
+   */
+  g_object_class_install_property (G_OBJECT_CLASS (klass),
+      PROP_MODE, g_param_spec_enum ("mode",
+          "Mode",
+          "Control whether and how detected CC meta should be inserted "
+          "in the list of existing CC meta on a frame (if any).",
+          GST_TYPE_LINE_21_DECODER_MODE, DEFAULT_MODE,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gst_element_class_set_static_metadata (gstelement_class,
       "Line 21 CC Decoder",
       "Filter/Video/ClosedCaption",
@@ -167,6 +227,7 @@ gst_line_21_decoder_init (GstLine21Decoder * filter)
   self->line21_offset = -1;
   self->max_line_probes = 40;
   self->ntsc_only = DEFAULT_NTSC_ONLY;
+  self->mode = DEFAULT_MODE;
 }
 
 static vbi_pixfmt
@@ -404,6 +465,15 @@ get_video_data (GstLine21Decoder * self, GstVideoFrame * frame, gint line)
   return self->converted_lines;
 }
 
+static gboolean
+drop_cc_meta (GstBuffer * buffer, GstMeta ** meta, gpointer unused)
+{
+  if ((*meta)->info->api == GST_VIDEO_CAPTION_META_API_TYPE)
+    *meta = NULL;
+
+  return TRUE;
+}
+
 /* Call this to scan for CC
  * Returns TRUE if it was found and set, else FALSE */
 static gboolean
@@ -414,6 +484,13 @@ gst_line_21_decoder_scan (GstLine21Decoder * self, GstVideoFrame * frame)
   gboolean found = FALSE;
   guint8 *data;
 
+  if (self->mode == GST_LINE_21_DECODER_MODE_DROP &&
+      gst_buffer_get_n_meta (frame->buffer,
+          GST_VIDEO_CAPTION_META_API_TYPE) > 0) {
+    GST_DEBUG_OBJECT (self, "Mode drop and buffer had CC meta, ignoring");
+    return FALSE;
+  }
+
   GST_DEBUG_OBJECT (self, "Starting probing. max_line_probes:%d",
       self->max_line_probes);
 
@@ -443,7 +520,6 @@ gst_line_21_decoder_scan (GstLine21Decoder * self, GstVideoFrame * frame)
   }
 
   if (!found) {
-    GST_DEBUG_OBJECT (self, "No CC found");
     self->line21_offset = -1;
   } else {
     guint base_line1 = 0, base_line2 = 0;
@@ -457,6 +533,12 @@ gst_line_21_decoder_scan (GstLine21Decoder * self, GstVideoFrame * frame)
       base_line2 = 318;
     }
 
+    if (self->mode == GST_LINE_21_DECODER_MODE_REPLACE) {
+      GST_DEBUG_OBJECT (self,
+          "Mode replace and new CC meta, removing existing CC meta");
+      gst_buffer_foreach_meta (frame->buffer, drop_cc_meta, NULL);
+    }
+
     ccdata[0] |= (base_line1 < i ? i - base_line1 : 0) & 0x1f;
     ccdata[1] = sliced[0].data[0];
     ccdata[2] = sliced[0].data[1];
diff --git a/ext/closedcaption/gstline21dec.h b/ext/closedcaption/gstline21dec.h
index c0134b304..edf140856 100644
--- a/ext/closedcaption/gstline21dec.h
+++ b/ext/closedcaption/gstline21dec.h
@@ -41,6 +41,12 @@ G_BEGIN_DECLS
 typedef struct _GstLine21Decoder GstLine21Decoder;
 typedef struct _GstLine21DecoderClass GstLine21DecoderClass;
 
+typedef enum {
+  GST_LINE_21_DECODER_MODE_ADD,
+  GST_LINE_21_DECODER_MODE_DROP,
+  GST_LINE_21_DECODER_MODE_REPLACE,
+} GstLine21DecoderMode;
+
 struct _GstLine21Decoder
 {
   GstVideoFilter parent;
@@ -62,6 +68,7 @@ struct _GstLine21Decoder
   GstVideoInfo *info;
 
   gboolean ntsc_only;
+  GstLine21DecoderMode mode;
 };
 
 struct _GstLine21DecoderClass