Display active tracks in OTel metrics (#1085)

* Add track, feed and transceiver spans under call span

src/otel/OTelCallTransceiverMediaStreamSpan.ts

@@ -0,0 +1,54 @@
+import { Span } from "@opentelemetry/api";
+import {
+  TrackStats,
+  TransceiverStats,
+} from "matrix-js-sdk/src/webrtc/stats/statsReport";
+
+import { ElementCallOpenTelemetry } from "./otel";
+import { OTelCallAbstractMediaStreamSpan } from "./OTelCallAbstractMediaStreamSpan";
+
+export class OTelCallTransceiverMediaStreamSpan extends OTelCallAbstractMediaStreamSpan {
+  private readonly prev: {
+    direction: string;
+    currentDirection: string;
+  };
+
+  constructor(
+    readonly oTel: ElementCallOpenTelemetry,
+    readonly callSpan: Span,
+    stats: TransceiverStats
+  ) {
+    super(oTel, callSpan, `matrix.call.transceiver.${stats.mid}`);
+    this.span.setAttribute("transceiver.mid", stats.mid);
+
+    this.prev = {
+      direction: stats.direction,
+      currentDirection: stats.currentDirection,
+    };
+    this.span.addEvent("matrix.call.transceiver.initState", this.prev);
+  }
+
+  public update(stats: TransceiverStats): void {
+    if (this.prev.currentDirection !== stats.currentDirection) {
+      this.span.addEvent("matrix.call.transceiver.currentDirection", {
+        currentDirection: stats.currentDirection,
+      });
+      this.prev.currentDirection = stats.currentDirection;
+    }
+    if (this.prev.direction !== stats.direction) {
+      this.span.addEvent("matrix.call.transceiver.direction", {
+        direction: stats.direction,
+      });
+      this.prev.direction = stats.direction;
+    }
+
+    const trackStats: TrackStats[] = [];
+    if (stats.sender) {
+      trackStats.push(stats.sender);
+    }
+    if (stats.receiver) {
+      trackStats.push(stats.receiver);
+    }
+    this.upsertTrackSpans(trackStats);
+  }
+}