fix(voice): start bitrate for non-SVC screen share codecs (#2434)

fluxer_app/pkgs/livekit-client/src/room/PCTransport.test.ts

@@ -0,0 +1,46 @@
+// SPDX-FileCopyrightText: 2024 LiveKit, Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+import type {MediaDescription} from 'sdp-transform';
+import {describe, expect, it} from 'vitest';
+import {appendStartBitrateToFmtp} from './PCTransport.ts';
+
+function mediaWithFmtp(entries: Array<{payload: number; config: string}>): MediaDescription {
+	return {fmtp: entries} as unknown as MediaDescription;
+}
+
+describe('appendStartBitrateToFmtp', () => {
+	it('appends the start bitrate to a non-SVC codec fmtp line', () => {
+		const media = mediaWithFmtp([
+			{payload: 96, config: 'level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42e01f'},
+		]);
+		appendStartBitrateToFmtp(media, 96, 2100);
+		expect(media.fmtp[0]?.config).toBe(
+			'level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42e01f;x-google-start-bitrate=2100',
+		);
+	});
+
+	it('only touches the fmtp line for the matching payload', () => {
+		const media = mediaWithFmtp([
+			{payload: 96, config: 'profile-level-id=42e01f'},
+			{payload: 98, config: 'profile-id=0'},
+		]);
+		appendStartBitrateToFmtp(media, 98, 1400);
+		expect(media.fmtp[0]?.config).toBe('profile-level-id=42e01f');
+		expect(media.fmtp[1]?.config).toBe('profile-id=0;x-google-start-bitrate=1400');
+	});
+
+	it('never appends a second start bitrate', () => {
+		const media = mediaWithFmtp([{payload: 96, config: 'profile-level-id=42e01f;x-google-start-bitrate=900'}]);
+		appendStartBitrateToFmtp(media, 96, 2100);
+		expect(media.fmtp[0]?.config).toBe('profile-level-id=42e01f;x-google-start-bitrate=900');
+	});
+
+	it('does nothing without a usable bitrate or a matching payload', () => {
+		const media = mediaWithFmtp([{payload: 96, config: 'profile-level-id=42e01f'}]);
+		appendStartBitrateToFmtp(media, 96, 0);
+		appendStartBitrateToFmtp(media, 96, -1);
+		appendStartBitrateToFmtp(media, 111, 2100);
+		expect(media.fmtp[0]?.config).toBe('profile-level-id=42e01f');
+	});
+});