perf(call): H.264 + contentHint + 30fps default for screen-share

The real cost in the "frame by frame" stutter wasn't the custom capture
path — it was LiveKit re-encoding via VP9 software with L3T3_KEY SVC
(three spatial × three temporal layers, all CPU). Switching the
per-publish codec to H.264 lets Chromium's hardware encoder take over
on Windows and sidesteps the SVC mode entirely (H.264 has no SVC).
Also pushes `contentHint = 'detail'` on the track — setScreenShareEnabled
does this internally, the manual publishTrack paths had been missing it,
which changes how the encoder allocates its frame budget for static UI
content.

Auto preset default framerate 60 → 30. 60fps desktop share burns three
full-res encodes per frame at sizes up to 4K; 30 is what getDisplayMedia
practically delivers anyway.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/context/CallContext.tsx

@@ -1310,9 +1310,17 @@ export function CallProvider({ children }: { children: ReactNode }) {
             stream.getTracks().forEach((t) => t.stop());
             throw new Error('no video track from chromeMediaSource');
           }
+          // H.264 lets Chromium's hardware encoder take over on Windows
+          // (Intel QuickSync / NVENC / AMD VCE) — VP9 is software-only in
+          // Chromium's WebRTC path and collapses under the L3T3_KEY
+          // scalability mode we set globally for camera. `contentHint` is
+          // what setScreenShareEnabled sets internally; pushing it by hand
+          // here tells the encoder to weight sharpness over smoothness,
+          // which is right for UI/text-heavy screen content.
+          videoMst.contentHint = 'detail';
           const videoPub = await lp.publishTrack(videoMst, {
             source: LkTrack.Source.ScreenShare,
-            videoCodec: 'vp9',
+            videoCodec: 'h264',
           });
           const audioRes = await startWasapiAudio(LkTrack);
           videoMst.addEventListener('ended', () => {
@@ -1358,9 +1366,10 @@ export function CallProvider({ children }: { children: ReactNode }) {
             nativeCaptureRef.current = null;
             throw new NativeCaptureUnavailable('canvas stream produced no video track');
           }
+          videoMst.contentHint = 'detail';
           const videoPub = await lp.publishTrack(videoMst, {
             source: LkTrack.Source.ScreenShare,
-            videoCodec: 'vp9',
+            videoCodec: 'h264',
           });
           const audioRes = await startWasapiAudio(LkTrack);
           videoMst.addEventListener('ended', () => {

apps/desktop/src/lib/screenShareSettings.ts

@@ -46,7 +46,7 @@ export interface PresetParams {
 }
 
 const PRESET_PARAMS: Record<ScreenSharePreset, PresetParams> = {
-  auto: { dims: null, framerate: 60, bitrateKbps: 8000, label: 'Auto (Original)' },
+  auto: { dims: null, framerate: 30, bitrateKbps: 8000, label: 'Auto (Original)' },
   '720p30': {
     dims: { width: 1280, height: 720 },
     framerate: 30,