webrtcsink: Added sinkpad with "msid" property

This forwards to the webrtcbin sinkpad's msid when specified.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1460>

docs/plugins/gst_plugins_cache.json

@@ -6704,12 +6704,14 @@
                     "audio_%%u": {
                         "caps": "audio/x-raw:\naudio/x-opus:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     },
                     "video_%%u": {
                         "caps": "video/x-raw:\n\nvideo/x-raw(memory:CUDAMemory):\n\nvideo/x-raw(memory:GLMemory):\n\nvideo/x-raw(memory:NVMM):\n\nvideo/x-raw(memory:D3D11Memory):\nvideo/x-vp8:\nvideo/x-h264:\nvideo/x-vp9:\nvideo/x-h265:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     }
                 },
                 "rank": "none"
@@ -6735,12 +6737,14 @@
                     "audio_%%u": {
                         "caps": "audio/x-raw:\naudio/x-opus:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     },
                     "video_%%u": {
                         "caps": "video/x-raw:\n\nvideo/x-raw(memory:CUDAMemory):\n\nvideo/x-raw(memory:GLMemory):\n\nvideo/x-raw(memory:NVMM):\n\nvideo/x-raw(memory:D3D11Memory):\nvideo/x-vp8:\nvideo/x-h264:\nvideo/x-vp9:\nvideo/x-h265:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     }
                 },
                 "rank": "none"
@@ -6766,12 +6770,14 @@
                     "audio_%%u": {
                         "caps": "audio/x-raw:\naudio/x-opus:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     },
                     "video_%%u": {
                         "caps": "video/x-raw:\n\nvideo/x-raw(memory:CUDAMemory):\n\nvideo/x-raw(memory:GLMemory):\n\nvideo/x-raw(memory:NVMM):\n\nvideo/x-raw(memory:D3D11Memory):\nvideo/x-vp8:\nvideo/x-h264:\nvideo/x-vp9:\nvideo/x-h265:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     }
                 },
                 "rank": "none"
@@ -6797,12 +6803,14 @@
                     "audio_%%u": {
                         "caps": "audio/x-raw:\naudio/x-opus:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     },
                     "video_%%u": {
                         "caps": "video/x-raw:\n\nvideo/x-raw(memory:CUDAMemory):\n\nvideo/x-raw(memory:GLMemory):\n\nvideo/x-raw(memory:NVMM):\n\nvideo/x-raw(memory:D3D11Memory):\nvideo/x-vp8:\nvideo/x-h264:\nvideo/x-vp9:\nvideo/x-h265:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     }
                 },
                 "rank": "none"
@@ -6862,12 +6870,14 @@
                     "audio_%%u": {
                         "caps": "audio/x-raw:\naudio/x-opus:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     },
                     "video_%%u": {
                         "caps": "video/x-raw:\n\nvideo/x-raw(memory:CUDAMemory):\n\nvideo/x-raw(memory:GLMemory):\n\nvideo/x-raw(memory:NVMM):\n\nvideo/x-raw(memory:D3D11Memory):\nvideo/x-vp8:\nvideo/x-h264:\nvideo/x-vp9:\nvideo/x-h265:\n",
                         "direction": "sink",
-                        "presence": "request"
+                        "presence": "request",
+                        "type": "GstWebRTCSinkPad"
                     }
                 },
                 "rank": "none"
@@ -7590,6 +7600,32 @@
                     }
                 ]
             },
+            "GstWebRTCSinkPad": {
+                "hierarchy": [
+                    "GstWebRTCSinkPad",
+                    "GstGhostPad",
+                    "GstProxyPad",
+                    "GstPad",
+                    "GstObject",
+                    "GInitiallyUnowned",
+                    "GObject"
+                ],
+                "kind": "object",
+                "properties": {
+                    "msid": {
+                        "blurb": "Remote MediaStream ID in use for this pad",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "NULL",
+                        "mutable": "ready",
+                        "readable": true,
+                        "type": "gchararray",
+                        "writable": true
+                    }
+                }
+            },
             "GstWebRTCSrcPad": {
                 "hierarchy": [
                     "GstWebRTCSrcPad",

net/webrtc/src/webrtcsink/imp.rs

@@ -20,7 +20,9 @@ use std::ops::Mul;
 use std::sync::{mpsc, Arc, Condvar, Mutex};
 
 use super::homegrown_cc::CongestionController;
-use super::{WebRTCSinkCongestionControl, WebRTCSinkError, WebRTCSinkMitigationMode};
+use super::{
+    WebRTCSinkCongestionControl, WebRTCSinkError, WebRTCSinkMitigationMode, WebRTCSinkPad,
+};
 use crate::aws_kvs_signaller::AwsKvsSignaller;
 use crate::janusvr_signaller::JanusVRSignaller;
 use crate::livekit_signaller::LiveKitSignaller;
@@ -186,7 +188,7 @@ impl futures::stream::FusedStream for CustomBusStream {
 /// Wrapper around our sink pads
 #[derive(Debug, Clone)]
 struct InputStream {
-    sink_pad: gst::GhostPad,
+    sink_pad: WebRTCSinkPad,
     producer: Option<StreamProducer>,
     /// The (fixed) caps coming in
     in_caps: Option<gst::Caps>,
@@ -1434,6 +1436,10 @@ impl InputStream {
             ),
         )
     }
+
+    fn msid(&self) -> Option<String> {
+        self.sink_pad.property("msid")
+    }
 }
 
 impl NavigationEventHandler {
@@ -1738,6 +1744,11 @@ impl BaseWebRTCSink {
                 return;
             };
 
+            if let Some(msid) = stream.msid() {
+                gst::trace!(CAT, obj: element, "forwarding msid={msid:?} to webrtcbin sinkpad");
+                pad.set_property("msid", &msid);
+            }
+
             let transceiver = pad.property::<gst_webrtc::WebRTCRTPTransceiver>("transceiver");
 
             transceiver.set_property(
@@ -4071,11 +4082,12 @@ impl ElementImpl for BaseWebRTCSink {
                 caps_builder = caps_builder.structure(codec.caps.structure(0).unwrap().to_owned());
             }
 
-            let video_pad_template = gst::PadTemplate::new(
+            let video_pad_template = gst::PadTemplate::with_gtype(
                 "video_%u",
                 gst::PadDirection::Sink,
                 gst::PadPresence::Request,
                 &caps_builder.build(),
+                WebRTCSinkPad::static_type(),
             )
             .unwrap();
 
@@ -4084,11 +4096,12 @@ impl ElementImpl for BaseWebRTCSink {
             for codec in Codecs::audio_codecs() {
                 caps_builder = caps_builder.structure(codec.caps.structure(0).unwrap().to_owned());
             }
-            let audio_pad_template = gst::PadTemplate::new(
+            let audio_pad_template = gst::PadTemplate::with_gtype(
                 "audio_%u",
                 gst::PadDirection::Sink,
                 gst::PadPresence::Request,
                 &caps_builder.build(),
+                WebRTCSinkPad::static_type(),
             )
             .unwrap();
 
@@ -4127,13 +4140,13 @@ impl ElementImpl for BaseWebRTCSink {
             (name, false)
         };
 
-        let sink_pad = gst::GhostPad::builder_from_template(templ)
+        let sink_pad = gst::PadBuilder::<WebRTCSinkPad>::from_template(templ)
             .name(name.as_str())
             .chain_function(|pad, parent, buffer| {
                 BaseWebRTCSink::catch_panic_pad_function(
                     parent,
                     || Err(gst::FlowError::Error),
-                    |this| this.chain(pad, buffer),
+                    |this| this.chain(pad.upcast_ref(), buffer),
                 )
             })
             .event_function(|pad, parent, event| {
@@ -4250,7 +4263,7 @@ impl ChildProxyImpl for BaseWebRTCSink {
     fn child_by_name(&self, name: &str) -> Option<glib::Object> {
         match name {
             "signaller" => Some(self.settings.lock().unwrap().signaller.clone().upcast()),
-            _ => None,
+            _ => self.obj().static_pad(name).map(|pad| pad.upcast()),
         }
     }
 }

net/webrtc/src/webrtcsink/mod.rs

@@ -39,11 +39,16 @@ use gst::subclass::prelude::*;
 mod homegrown_cc;
 
 mod imp;
+mod pad;
 
 glib::wrapper! {
     pub struct BaseWebRTCSink(ObjectSubclass<imp::BaseWebRTCSink>) @extends gst::Bin, gst::Element, gst::Object, @implements gst::ChildProxy, gst_video::Navigation;
 }
 
+glib::wrapper! {
+    pub struct WebRTCSinkPad(ObjectSubclass<pad::WebRTCSinkPad>) @extends gst::GhostPad, gst::ProxyPad, gst::Pad, gst::Object;
+}
+
 glib::wrapper! {
     pub struct WebRTCSink(ObjectSubclass<imp::WebRTCSink>) @extends BaseWebRTCSink, gst::Bin, gst::Element, gst::Object, @implements gst::ChildProxy, gst_video::Navigation;
 }
@@ -124,6 +129,7 @@ enum WebRTCSinkMitigationMode {
 }
 
 pub fn register(plugin: &gst::Plugin) -> Result<(), glib::BoolError> {
+    WebRTCSinkPad::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
     BaseWebRTCSink::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
     WebRTCSinkCongestionControl::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
     gst::Element::register(

net/webrtc/src/webrtcsink/pad.rs

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use gst::{glib, prelude::*, subclass::prelude::*};
+use once_cell::sync::Lazy;
+use std::sync::Mutex;
+
+#[derive(Default)]
+pub struct WebRTCSinkPad {
+    settings: Mutex<Settings>,
+}
+
+#[derive(Debug, Default)]
+struct Settings {
+    msid: Option<String>,
+}
+
+#[glib::object_subclass]
+impl ObjectSubclass for WebRTCSinkPad {
+    const NAME: &'static str = "GstWebRTCSinkPad";
+    type Type = super::WebRTCSinkPad;
+    type ParentType = gst::GhostPad;
+}
+
+impl ObjectImpl for WebRTCSinkPad {
+    fn properties() -> &'static [glib::ParamSpec] {
+        static PROPS: Lazy<Vec<glib::ParamSpec>> = Lazy::new(|| {
+            vec![glib::ParamSpecString::builder("msid")
+                .flags(glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY)
+                .blurb("Remote MediaStream ID in use for this pad")
+                .build()]
+        });
+        PROPS.as_ref()
+    }
+    fn set_property(&self, _id: usize, value: &glib::Value, pspec: &glib::ParamSpec) {
+        let mut settings = self.settings.lock().unwrap();
+        match pspec.name() {
+            "msid" => {
+                settings.msid = value
+                    .get::<Option<String>>()
+                    .expect("type checked upstream")
+            }
+            name => panic!("no writable property {name:?}"),
+        }
+    }
+    fn property(&self, _id: usize, pspec: &glib::ParamSpec) -> glib::Value {
+        let settings = self.settings.lock().unwrap();
+        match pspec.name() {
+            "msid" => settings.msid.to_value(),
+            name => panic!("no readable property {name:?}"),
+        }
+    }
+}
+
+impl GstObjectImpl for WebRTCSinkPad {}
+impl PadImpl for WebRTCSinkPad {}
+impl ProxyPadImpl for WebRTCSinkPad {}
+impl GhostPadImpl for WebRTCSinkPad {}