enable screen share simulcast by default (#156)

src/room/participant/LocalParticipant.ts

@@ -17,7 +17,8 @@ import LocalVideoTrack, { videoLayersFromEncodings } from '../track/LocalVideoTr
 import {
   CreateLocalTracksOptions,
   ScreenShareCaptureOptions,
-  TrackPublishOptions, VideoCodec, VideoPresets,
+  ScreenSharePresets,
+  TrackPublishOptions, VideoCodec,
 } from '../track/options';
 import { Track } from '../track/Track';
 import { constraintsForOptions, mergeDefaultOptions } from '../track/utils';
@@ -272,7 +273,7 @@ export default class LocalParticipant extends Participant {
       options = {};
     }
     if (options.resolution === undefined) {
-      options.resolution = VideoPresets.fhd.resolution;
+      options.resolution = ScreenSharePresets.h720fps15.resolution;
     }
 
     let videoConstraints: MediaTrackConstraints | boolean = true;

src/room/participant/publishUtils.test.ts

@@ -1,5 +1,8 @@
-import { VideoPreset, VideoPresets, VideoPresets43 } from '../track/options';
 import {
+  ScreenSharePresets, VideoPreset, VideoPresets, VideoPresets43,
+} from '../track/options';
+import {
+  computeDefaultScreenShareSimulcastPresets,
   computeVideoEncodings,
   determineAppropriateEncoding,
   presets169,
@@ -128,3 +131,15 @@ describe('customSimulcastLayers', () => {
     expect(sortedPresets[2].encoding.maxFramerate).toBe(20);
   });
 });
+
+describe('screenShareSimulcastDefaults', () => {
+  it('computes appropriate bitrate from original preset', () => {
+    const defaultSimulcastLayers = computeDefaultScreenShareSimulcastPresets(
+      ScreenSharePresets.h720fps15,
+    );
+    expect(defaultSimulcastLayers[0].width).toBe(640);
+    expect(defaultSimulcastLayers[0].height).toBe(360);
+    expect(defaultSimulcastLayers[0].encoding.maxFramerate).toBe(3);
+    expect(defaultSimulcastLayers[0].encoding.maxBitrate).toBe(150_000);
+  });
+});

src/room/participant/publishUtils.ts

@@ -46,6 +46,18 @@ export const defaultSimulcastPresets43 = [
   VideoPresets43.h360,
 ];
 
+/* @internal */
+export const computeDefaultScreenShareSimulcastPresets = (fromPreset: VideoPreset) => {
+  const layers = [{ scaleResolutionDownBy: 2, fps: 3 }];
+  return layers.map((t) => new VideoPreset(
+    Math.floor(fromPreset.width / t.scaleResolutionDownBy),
+    Math.floor(fromPreset.height / t.scaleResolutionDownBy),
+    Math.max(150_000, Math.floor(fromPreset.encoding.maxBitrate
+      / (t.scaleResolutionDownBy ** 2 * ((fromPreset.encoding.maxFramerate ?? 30) / t.fps)))),
+    t.fps,
+  ));
+};
+
 const videoRids = ['q', 'h', 'f'];
 
 /* @internal */
@@ -59,9 +71,7 @@ export function computeVideoEncodings(
   if (isScreenShare) {
     videoEncoding = options?.screenShareEncoding;
   }
-  // only use simulcast for screenshares if the simulcast layers are provided via config
-  const useSimulcast = (!isScreenShare || options?.screenShareSimulcastLayers)
-    && options?.simulcast;
+  const useSimulcast = options?.simulcast;
 
   if ((!videoEncoding && !useSimulcast) || !width || !height) {
     // when we aren't simulcasting, will need to return a single encoding without
@@ -78,22 +88,22 @@ export function computeVideoEncodings(
   if (!useSimulcast) {
     return [videoEncoding];
   }
+  const original = new VideoPreset(
+    width, height, videoEncoding.maxBitrate, videoEncoding.maxFramerate,
+  );
   let presets: Array<VideoPreset> = [];
   if (isScreenShare) {
     presets = sortPresets(options?.screenShareSimulcastLayers)
-      ?? defaultSimulcastLayers(isScreenShare, width, height);
+      ?? defaultSimulcastLayers(isScreenShare, original);
   } else {
     presets = sortPresets(options?.videoSimulcastLayers)
-      ?? defaultSimulcastLayers(isScreenShare, width, height);
+      ?? defaultSimulcastLayers(isScreenShare, original);
   }
   let midPreset: VideoPreset | undefined;
   const lowPreset = presets[0];
   if (presets.length > 1) {
     [, midPreset] = presets;
   }
-  const original = new VideoPreset(
-    width, height, videoEncoding.maxBitrate, videoEncoding.maxFramerate,
-  );
 
   // NOTE:
   //   1. Ordering of these encodings is important. Chrome seems
@@ -159,11 +169,12 @@ export function presetsForResolution(
 
 /* @internal */
 export function defaultSimulcastLayers(
-  isScreenShare: boolean, width: number, height: number,
+  isScreenShare: boolean, original: VideoPreset,
 ): VideoPreset[] {
   if (isScreenShare) {
-    return [];
+    return computeDefaultScreenShareSimulcastPresets(original);
   }
+  const { width, height } = original;
   const aspect = width > height ? width / height : height / width;
   if (Math.abs(aspect - 16.0 / 9) < Math.abs(aspect - 4.0 / 3)) {
     return defaultSimulcastPresets169;

src/room/track/defaults.ts

@@ -7,7 +7,7 @@ export const publishDefaults: TrackPublishDefaults = {
   audioBitrate: AudioPresets.speech.maxBitrate,
   dtx: true,
   simulcast: true,
-  screenShareEncoding: ScreenSharePresets.hd_15.encoding,
+  screenShareEncoding: ScreenSharePresets.h720fps15.encoding,
   stopMicTrackOnMute: false,
 };
 
@@ -19,5 +19,5 @@ export const audioDefaults: AudioCaptureOptions = {
 };
 
 export const videoDefaults: VideoCaptureOptions = {
-  resolution: VideoPresets.qhd.resolution,
+  resolution: VideoPresets.h540.resolution,
 };