Display active tracks in OTel metrics (#1085)

* Add track, feed and transceiver spans under call span

src/otel/OTelCallMediaStreamTrackSpan.ts

@@ -0,0 +1,62 @@
+import { TrackStats } from "matrix-js-sdk/src/webrtc/stats/statsReport";
+import opentelemetry, { Span } from "@opentelemetry/api";
+
+import { ElementCallOpenTelemetry } from "./otel";
+
+export class OTelCallMediaStreamTrackSpan {
+  private readonly span: Span;
+  private prev: TrackStats;
+
+  public constructor(
+    readonly oTel: ElementCallOpenTelemetry,
+    readonly streamSpan: Span,
+    data: TrackStats
+  ) {
+    const ctx = opentelemetry.trace.setSpan(
+      opentelemetry.context.active(),
+      streamSpan
+    );
+    const options = {
+      links: [
+        {
+          context: streamSpan.spanContext(),
+        },
+      ],
+    };
+    const type = `matrix.call.track.${data.label}.${data.kind}`;
+    this.span = oTel.tracer.startSpan(type, options, ctx);
+    this.span.setAttribute("track.trackId", data.id);
+    this.span.setAttribute("track.kind", data.kind);
+    this.span.setAttribute("track.constrainDeviceId", data.constrainDeviceId);
+    this.span.setAttribute("track.settingDeviceId", data.settingDeviceId);
+    this.span.setAttribute("track.label", data.label);
+
+    this.span.addEvent("matrix.call.track.initState", {
+      readyState: data.readyState,
+      muted: data.muted,
+      enabled: data.enabled,
+    });
+    this.prev = data;
+  }
+
+  public update(data: TrackStats): void {
+    if (this.prev.muted !== data.muted) {
+      this.span.addEvent("matrix.call.track.muted", { muted: data.muted });
+    }
+    if (this.prev.enabled !== data.enabled) {
+      this.span.addEvent("matrix.call.track.enabled", {
+        enabled: data.enabled,
+      });
+    }
+    if (this.prev.readyState !== data.readyState) {
+      this.span.addEvent("matrix.call.track.readyState", {
+        readyState: data.readyState,
+      });
+    }
+    this.prev = data;
+  }
+
+  public end(): void {
+    this.span.end();
+  }
+}