Fix race condition of _startTime

src/media/BaseMediaStream.ts

@@ -1,4 +1,5 @@
 import { Log } from "debug-level";
+import { setImmediate } from "node:timers";
 import { setTimeout } from "node:timers/promises";
 import { Writable } from "node:stream";
 import { combineLoHi } from "./utils.js";
@@ -32,8 +33,19 @@ export class BaseMediaStream extends Writable {
         if (val)
         {
             // Reset timestamp stats when enabling sync
-            this._startPts = this._startTime = undefined;
-            this._loggerSync.debug("Sync enabled");
+            /**
+             * Since _waitForOtherStream() is an async function, it can only
+             * return at the end of the event loop, while Node.js is processing
+             * the microtask queue. If this is run synchronously, it can set
+             * _startTime to undefined before _waitForOtherStream() returns,
+             * which will cause the timeout calculation below to return NaN.
+             * Use setImmediate to put this on the macrotask queue, which is
+             * processed after the microtask queue.
+             */
+            setImmediate(() => {
+                this._startPts = this._startTime = undefined;
+                this._loggerSync.debug("Sync enabled");
+            });
         }
         else
         {