rtpopusdepay: support libwebrtc-compatible multichannel payload

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/832>

gst/rtp/gstrtpopusdepay.c

@@ -41,14 +41,14 @@ GST_STATIC_PAD_TEMPLATE ("sink",
         "media = (string) \"audio\", "
         "payload = (int) " GST_RTP_PAYLOAD_DYNAMIC_STRING ","
         "clock-rate = (int) 48000, "
-        "encoding-name = (string) { \"OPUS\", \"X-GST-OPUS-DRAFT-SPITTKA-00\" }")
+        "encoding-name = (string) { \"OPUS\", \"X-GST-OPUS-DRAFT-SPITTKA-00\", \"multiopus\" }")
     );
 
 static GstStaticPadTemplate gst_rtp_opus_depay_src_template =
 GST_STATIC_PAD_TEMPLATE ("src",
     GST_PAD_SRC,
     GST_PAD_ALWAYS,
-    GST_STATIC_CAPS ("audio/x-opus, channel-mapping-family = (int) 0")
+    GST_STATIC_CAPS ("audio/x-opus, channel-mapping-family = (int) [ 0, 1 ]")
     );
 
 static GstBuffer *gst_rtp_opus_depay_process (GstRTPBaseDepayload * depayload,
@@ -96,21 +96,116 @@ gst_rtp_opus_depay_setcaps (GstRTPBaseDepayload * depayload, GstCaps * caps)
   GstCaps *srccaps;
   GstStructure *s;
   gboolean ret;
-  const gchar *sprop_stereo, *sprop_maxcapturerate;
+  const gchar *sprop_maxcapturerate;
 
-  srccaps =
+  srccaps = gst_caps_new_empty_simple ("audio/x-opus");
-      gst_caps_new_simple ("audio/x-opus", "channel-mapping-family", G_TYPE_INT,
-      0, NULL);
 
   s = gst_caps_get_structure (caps, 0);
-  if ((sprop_stereo = gst_structure_get_string (s, "sprop-stereo"))) {
+
-    if (strcmp (sprop_stereo, "0") == 0)
+  if (g_str_equal (gst_structure_get_string (s, "encoding-name"), "multiopus")) {
+    gint channels;
+    gint stream_count;
+    gint coupled_count;
+    const gchar *encoding_params;
+    const gchar *num_streams;
+    const gchar *coupled_streams;
+    const gchar *channel_mapping;
+    gchar *endptr;
+
+    if (!gst_structure_has_field_typed (s, "encoding-params", G_TYPE_STRING) ||
+        !gst_structure_has_field_typed (s, "num_streams", G_TYPE_STRING) ||
+        !gst_structure_has_field_typed (s, "coupled_streams", G_TYPE_STRING) ||
+        !gst_structure_has_field_typed (s, "channel_mapping", G_TYPE_STRING)) {
+      GST_WARNING_OBJECT (depayload, "Encoding name 'multiopus' requires "
+          "encoding-params, num_streams, coupled_streams and channel_mapping "
+          "as string fields in caps.");
+      goto reject_caps;
+    }
+
+    gst_caps_set_simple (srccaps, "channel-mapping-family", G_TYPE_INT, 1,
+        NULL);
+
+    encoding_params = gst_structure_get_string (s, "encoding-params");
+    channels = g_ascii_strtoull (encoding_params, &endptr, 10);
+    if (*endptr != '\0' || channels > 255) {
+      GST_WARNING_OBJECT (depayload, "Invalid encoding-params value '%s'",
+          encoding_params);
+      goto reject_caps;
+    }
+    gst_caps_set_simple (srccaps, "channels", G_TYPE_INT, channels, NULL);
+
+    num_streams = gst_structure_get_string (s, "num_streams");
+    stream_count = g_ascii_strtoull (num_streams, &endptr, 10);
+    if (*endptr != '\0' || stream_count > channels) {
+      GST_WARNING_OBJECT (depayload, "Invalid num_streams value '%s'",
+          num_streams);
+      goto reject_caps;
+    }
+    gst_caps_set_simple (srccaps, "stream-count", G_TYPE_INT, stream_count,
+        NULL);
+
+    coupled_streams = gst_structure_get_string (s, "coupled_streams");
+    coupled_count = g_ascii_strtoull (coupled_streams, &endptr, 10);
+    if (*endptr != '\0' || coupled_count > stream_count) {
+      GST_WARNING_OBJECT (depayload, "Invalid coupled_streams value '%s'",
+          coupled_streams);
+      goto reject_caps;
+    }
+    gst_caps_set_simple (srccaps, "coupled-count", G_TYPE_INT, coupled_count,
+        NULL);
+
+    channel_mapping = gst_structure_get_string (s, "channel_mapping");
+    {
+      gchar **split;
+      gchar **ptr;
+      GValue mapping = G_VALUE_INIT;
+      GValue v = G_VALUE_INIT;
+
+      split = g_strsplit (channel_mapping, ",", -1);
+
+      g_value_init (&mapping, GST_TYPE_ARRAY);
+      g_value_init (&v, G_TYPE_INT);
+
+      for (ptr = split; *ptr; ++ptr) {
+        gint channel = g_ascii_strtoull (*ptr, &endptr, 10);
+        if (*endptr != '\0' || channel > channels) {
+          GST_WARNING_OBJECT (depayload, "Invalid channel_mapping value '%s'",
+              channel_mapping);
+          g_value_unset (&mapping);
+          break;
+        }
+        g_value_set_int (&v, channel);
+        gst_value_array_append_value (&mapping, &v);
+      }
+
+      g_value_unset (&v);
+      g_strfreev (split);
+
+      if (G_IS_VALUE (&mapping)) {
+        gst_caps_set_value (srccaps, "channel-mapping", &mapping);
+        g_value_unset (&mapping);
+      } else {
+        goto reject_caps;
+      }
+    }
+  } else {
+    const gchar *sprop_stereo;
+
+    gst_caps_set_simple (srccaps, "channel-mapping-family", G_TYPE_INT, 0,
+        NULL);
+
+    if ((sprop_stereo = gst_structure_get_string (s, "sprop-stereo"))) {
+      if (strcmp (sprop_stereo, "0") == 0)
+        gst_caps_set_simple (srccaps, "channels", G_TYPE_INT, 1, NULL);
+      else if (strcmp (sprop_stereo, "1") == 0)
+        gst_caps_set_simple (srccaps, "channels", G_TYPE_INT, 2, NULL);
+      else
+        GST_WARNING_OBJECT (depayload, "Unknown sprop-stereo value '%s'",
+            sprop_stereo);
+    } else {
+      /* sprop-stereo defaults to mono as per RFC 7587. */
       gst_caps_set_simple (srccaps, "channels", G_TYPE_INT, 1, NULL);
-    else if (strcmp (sprop_stereo, "1") == 0)
+    }
-      gst_caps_set_simple (srccaps, "channels", G_TYPE_INT, 2, NULL);
-    else
-      GST_WARNING_OBJECT (depayload, "Unknown sprop-stereo value '%s'",
-          sprop_stereo);
   }
 
   if ((sprop_maxcapturerate =
@@ -137,6 +232,11 @@ gst_rtp_opus_depay_setcaps (GstRTPBaseDepayload * depayload, GstCaps * caps)
   depayload->clock_rate = 48000;
 
   return ret;
+
+reject_caps:
+  gst_caps_unref (srccaps);
+
+  return FALSE;
 }
 
 static GstBuffer *