decklinkaudiosrc: Option to use max channels supported by device

Query the device for the maximum number of channels supported and have
an option to use that. Default is still 2.

https://bugzilla.gnome.org/show_bug.cgi?id=777458

sys/decklink/gstdecklink.cpp

@@ -200,6 +200,7 @@ gst_decklink_audio_channels_get_type (void)
     {GST_DECKLINK_AUDIO_CHANNELS_2, "2 Channels", "2"},
     {GST_DECKLINK_AUDIO_CHANNELS_8, "8 Channels", "8"},
     {GST_DECKLINK_AUDIO_CHANNELS_16, "16 Channels", "16"},
+    {GST_DECKLINK_AUDIO_CHANNELS_MAX, "Maximum channels supported", "max"},
     {0, NULL, NULL}
   };
 

sys/decklink/gstdecklink.h

@@ -111,6 +111,7 @@ typedef enum {
 GType gst_decklink_audio_connection_get_type (void);
 
 typedef enum {
+  GST_DECKLINK_AUDIO_CHANNELS_MAX = 0,
   GST_DECKLINK_AUDIO_CHANNELS_2 = 2,
   GST_DECKLINK_AUDIO_CHANNELS_8 = 8,
   GST_DECKLINK_AUDIO_CHANNELS_16 = 16

sys/decklink/gstdecklinkaudiosrc.cpp

@@ -427,10 +427,11 @@ gst_decklink_audio_src_get_caps (GstBaseSrc * bsrc, GstCaps * filter)
 
   if (!caps) {
     GstCaps *channel_filter, *templ;
+
     templ = gst_pad_get_pad_template_caps (GST_BASE_SRC_PAD (bsrc));
     channel_filter =
         gst_caps_new_simple ("audio/x-raw", "channels", G_TYPE_INT,
-        self->channels, NULL);
+        self->channels_found, NULL);
     caps = gst_caps_intersect (channel_filter, templ);
     gst_caps_unref (channel_filter);
     gst_caps_unref (templ);
@@ -736,6 +737,23 @@ gst_decklink_audio_src_open (GstDecklinkAudioSrc * self)
   }
 
   g_mutex_lock (&self->input->lock);
+  if (self->channels > 0) {
+    self->channels_found = self->channels;
+  } else {
+    if (self->input->attributes) {
+      HRESULT ret = self->input->attributes->GetInt
+          (BMDDeckLinkMaximumAudioChannels, &self->channels_found);
+      /* Sometimes the card may report an invalid number of channels. In
+       * that case, we should (empirically) use 8. */
+      if (ret != S_OK ||
+          self->channels_found == 0 || g_enum_get_value ((GEnumClass *)
+              g_type_class_peek (GST_TYPE_DECKLINK_AUDIO_CHANNELS),
+              self->channels_found)
+          == NULL) {
+        self->channels_found = GST_DECKLINK_AUDIO_CHANNELS_8;
+      }
+    }
+  }
   self->input->got_audio_packet = gst_decklink_audio_src_got_packet;
   g_mutex_unlock (&self->input->lock);
 

sys/decklink/gstdecklinkaudiosrc.h

@@ -53,6 +53,7 @@ struct _GstDecklinkAudioSrc
   GstDecklinkAudioConnectionEnum connection;
   gint device_number;
   GstDecklinkAudioChannelsEnum channels;
+  gint64 channels_found;
 
   GstAudioInfo info;