feat(gstreamer): integrate webrtc plugin (#9799)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

docs/src/libs/video_support/gstreamer.rst

@@ -27,6 +27,7 @@ LVGL's GStreamer implementation provides comprehensive media playback capabiliti
 * Video4Linux2 (V4L2) camera devices on Linux
 * Audio capture from ALSA and PulseAudio devices
 * Test sources for audio and video development
+* WebRTC streaming for real-time communication applications
 
 **URI Scheme Support:**
 
@@ -42,6 +43,10 @@ Using the URI factory (:c:macro:`LV_GSTREAMER_FACTORY_URI_DECODE`), you can spec
 
 GStreamer's ``uridecodebin`` automatically selects the appropriate source element and decoder based on the URI scheme and media format.
 
+.. note::
+
+   WebRTC streaming is supported via a dedicated WebRTC source factory (for example, ``webrtcsrc``) configured with a signalling URI (for example, ``signaller::uri``), and is not provided through :c:macro:`LV_GSTREAMER_FACTORY_URI_DECODE` / ``uridecodebin``.
+
 **Playback Control:**
 
 * Play, pause, and stop operations
@@ -255,6 +260,15 @@ The GStreamer widget supports various media sources through different factories:
                          "/path/to/video.mp4");
 
 
+**WebRTC Factory:**
+
+.. code-block:: c
+
+    /* WebRTC stream */
+    lv_gstreamer_set_src(streamer, LV_GSTREAMER_FACTORY_WEBRTCSRC,
+                         LV_GSTREAMER_PROPERTY_WEBRTCSRC,
+                         "ws://signalserver:port/");
+
 Playback Control
 ----------------
 
@@ -326,6 +340,20 @@ Once media is loaded (LV_EVENT_READY), you can access:
 - Current volume level via ``lv_gstreamer_get_volume()``
 - Current playback state via ``lv_gstreamer_get_state()``
 
+WebRTC Notes
+************
+
+WebRTC is using the Rust plugin "https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs"
+So to be able to stream to an LVGL player application you will need to run a signaller server and then a simpler pipeline like so:
+
+.. code-block:: bash
+
+    ./gst-webrtc-signalling-server &
+    gst-launch-1.0 videotestsrc pattern=ball ! webrtcsink
+
+Then, in your LVGL application, configure WebRTC by passing the signalling server URI (for example, ``ws://localhost:8443``) to ``lv_gstreamer_set_src(..., LV_GSTREAMER_PROPERTY_WEBRTCSRC, ...)``.
+
+
 .. _gstreamer_example:
 
 Example

examples/libs/gstreamer/lv_example_gstreamer_1.c

@@ -40,7 +40,11 @@ void lv_example_gstreamer_1(void)
      * specify various URI schemes as media sources including local files (file://),
      * web streams (http://, https://), RTSP streams (rtsp://), UDP streams (udp://),
      * and many others. GStreamer's uridecodebin automatically selects the appropriate
-     * source element and decoder based on the URI scheme and media format. */
+     * source element and decoder based on the URI scheme and media format.
+     * WebRTC streams, however, are provided via a dedicated WebRTC source (webrtcsrc)
+     * configured with a signalling server URI (e.g. ws://[ipsignallerserver]:[port])
+     * through its signaller-related properties, rather than via LV_GSTREAMER_FACTORY_URI_DECODE.
+     */
     lv_gstreamer_set_src(event_data.streamer, LV_GSTREAMER_FACTORY_URI_DECODE, LV_GSTREAMER_PROPERTY_URI_DECODE,
                          "https://gstreamer.freedesktop.org/data/media/sintel_trailer-480p.webm");
 

src/libs/gstreamer/lv_gstreamer.c

@@ -47,6 +47,8 @@ static void gstreamer_update_frame(lv_gstreamer_t * streamer);
 static lv_result_t gstreamer_make_and_add_to_pipeline(lv_gstreamer_t * streamer,
                                                       const lv_gstreamer_pipeline_element_t * elements, size_t element_count);
 static lv_result_t gstreamer_send_state_changed(lv_gstreamer_t * streamer, lv_gstreamer_stream_state_t state);
+static bool gstreamer_element_has_property(GstElement * element, const char * property_name);
+static bool gstreamer_set_child_proxy_string(GstElement * element, const char * property_name, const char * value);
 
 /**********************
  *  STATIC VARIABLES
@@ -135,31 +137,53 @@ lv_result_t lv_gstreamer_set_src(lv_obj_t * obj, const char * factory_name, cons
     }
 
     if(property != NULL && source != NULL) {
-        g_object_set(G_OBJECT(head), property, source, NULL);
+        /* LV_GSTREAMER_PROPERTY_WEBRTCSRC is a child-proxy property path */
+        if(lv_streq(property, LV_GSTREAMER_PROPERTY_WEBRTCSRC)) {
+            if(!gstreamer_set_child_proxy_string(head, property, source)) {
+                gst_object_unref(pipeline);
+                LV_LOG_ERROR("Failed to set '%s' via child proxy", property);
+                return LV_RESULT_INVALID;
+            }
+        }
+        else {
+            g_object_set(G_OBJECT(head), property, source, NULL);
+        }
     }
 
     /* The uri decode source element will automatically handle parsing and decoding for us
      * for other source types, we need to add a parser and a decoder ourselves element*/
     if(!lv_streq(LV_GSTREAMER_FACTORY_URI_DECODE, factory_name)) {
-        GstElement * decodebin = gst_element_factory_make("decodebin", "lv_gstreamer_decodebin");
-        if(!decodebin) {
-            gst_object_unref(pipeline);
-            LV_LOG_ERROR("Failed to create decodebin element");
-            return LV_RESULT_INVALID;
-        }
-        if(!gst_bin_add(GST_BIN(pipeline), decodebin)) {
-            gst_object_unref(decodebin);
-            gst_object_unref(pipeline);
-            LV_LOG_ERROR("Failed to add decodebin element to pipeline");
-            return LV_RESULT_INVALID;
+        /* webrtcsrc plugins require its own handling to be able to connect on the first available video stream */
+        if(lv_streq(LV_GSTREAMER_FACTORY_WEBRTCSRC, factory_name)) {
+            LV_LOG_INFO("Setting up webrtc pipeline");
+            if(gstreamer_element_has_property(head, "connect-to-first-producer")) {
+                g_object_set(G_OBJECT(head), "connect-to-first-producer", TRUE, NULL);
+            }
+            else {
+                LV_LOG_WARN("webrtcsrc property 'connect-to-first-producer' is not available in this plugin build");
+            }
         }
+        else {
+            GstElement * decodebin = gst_element_factory_make("decodebin", "lv_gstreamer_decodebin");
+            if(!decodebin) {
+                gst_object_unref(pipeline);
+                LV_LOG_ERROR("Failed to create decodebin element");
+                return LV_RESULT_INVALID;
+            }
+            if(!gst_bin_add(GST_BIN(pipeline), decodebin)) {
+                gst_object_unref(decodebin);
+                gst_object_unref(pipeline);
+                LV_LOG_ERROR("Failed to add decodebin element to pipeline");
+                return LV_RESULT_INVALID;
+            }
 
-        if(!gst_element_link(head, decodebin)) {
-            gst_object_unref(pipeline);
-            LV_LOG_ERROR("Failed to link source with parsebin elements");
-            return LV_RESULT_INVALID;
+            if(!gst_element_link(head, decodebin)) {
+                gst_object_unref(pipeline);
+                LV_LOG_ERROR("Failed to link source with parsebin elements");
+                return LV_RESULT_INVALID;
+            }
+            head = decodebin;
         }
-        head = decodebin;
     }
 
     /* At this point we don't yet know the input format
@@ -412,7 +436,18 @@ static lv_result_t gstreamer_poll_bus(lv_gstreamer_t * streamer)
                     GError * err;
                     gchar * debug;
                     gst_message_parse_error(msg, &err, &debug);
-                    LV_LOG_ERROR("GStreamer error: %s", err->message);
+                    GstObject * src = GST_MESSAGE_SRC(msg);
+                    const gchar * name = NULL;
+                    if(src != NULL) {
+                        name = GST_OBJECT_NAME(src);
+                    }
+                    if(!name) {
+                        name = "unknown";
+                    }
+                    LV_LOG_ERROR("GStreamer error from %s: %s", name, err->message);
+                    if(debug && debug[0] != '\0') {
+                        LV_LOG_ERROR("GStreamer error details: %s", debug);
+                    }
                     g_error_free(err);
                     g_free(debug);
                     break;
@@ -563,11 +598,50 @@ static lv_result_t gstreamer_make_and_add_to_pipeline(lv_gstreamer_t * streamer,
     return LV_RESULT_OK;
 }
 
+static bool gstreamer_element_has_property(GstElement * element, const char * property_name)
+{
+    LV_ASSERT_NULL(element);
+    LV_ASSERT_NULL(property_name);
+
+    GObjectClass * klass = G_OBJECT_GET_CLASS(element);
+    return g_object_class_find_property(klass, property_name) != NULL;
+}
+
+static bool gstreamer_set_child_proxy_string(GstElement * element, const char * property_name, const char * value)
+{
+    LV_ASSERT_NULL(element);
+    LV_ASSERT_NULL(property_name);
+    LV_ASSERT_NULL(value);
+
+    if(!GST_IS_CHILD_PROXY(element)) {
+        LV_LOG_WARN("Element does not support child proxy for property '%s'", property_name);
+        return false;
+    }
+
+    GObject * target = NULL;
+    GParamSpec * pspec = NULL;
+    if(!gst_child_proxy_lookup(GST_CHILD_PROXY(element), property_name, &target, &pspec)) {
+        LV_LOG_WARN("Property '%s' not found in child proxy", property_name);
+        return false;
+    }
+
+    if(target) {
+        g_object_unref(target);
+    }
+
+    GValue gvalue = G_VALUE_INIT;
+    g_value_init(&gvalue, G_TYPE_STRING);
+    g_value_set_string(&gvalue, value);
+    gst_child_proxy_set_property(GST_CHILD_PROXY(element), property_name, &gvalue);
+    g_value_unset(&gvalue);
+    return true;
+}
+
 static void on_decode_pad_added(GstElement * element, GstPad * pad, gpointer user_data)
 {
     LV_UNUSED(element);
     lv_gstreamer_t * streamer = (lv_gstreamer_t *)user_data;
-    GstCaps * caps = gst_pad_get_current_caps(pad);
+    GstCaps * caps = gst_pad_query_caps(pad, NULL);
 
     GstStructure * structure = gst_caps_get_structure(caps, 0);
     const gchar * name = gst_structure_get_name(structure);

src/libs/gstreamer/lv_gstreamer.h

@@ -62,6 +62,9 @@ extern "C" {
 #define LV_GSTREAMER_FACTORY_APP             "appsrc"
 #define LV_GSTREAMER_PROPERTY_APP             NULL
 
+#define LV_GSTREAMER_FACTORY_WEBRTCSRC       "webrtcsrc"
+#define LV_GSTREAMER_PROPERTY_WEBRTCSRC      "signaller::uri"
+
 /**********************
  *      TYPEDEFS
  **********************/