Fix video codec, aspect and placement

Three problems visible at once on a running instance: the picture
stuttered and drifted behind the sound, it was letterboxed oddly, and it
appeared as a separate tile instead of coming from the bot.

- YouTube handed us AV1 (format 398). Software-decoding AV1 at 720p does
  not sustain real time on a small server, which explains both the
  stutter and the drift; H.264 is now requested first, VP9 second.
- The frame was padded into a fixed box, so a clip whose proportions
  differed got black bars baked in and then more from the client. Size is
  now a bounding box and the frame keeps the clip's own proportions.
- Video was published as a screen share, which every client renders as
  its own tile. VIDEO_SOURCE=camera (the new default) puts it inside the
  bot's tile; "screen" keeps the old behaviour.

VIDEO_SYNC_OFFSET_MS is there for the residual drift, since audio and
video travel as two separately published tracks. Measured loudnorm first
to rule it out as the cause of the desync: it adds 0 ms.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/video.ts

@@ -1,6 +1,7 @@
 import { createRequire } from "node:module";
 import type { Readable } from "node:stream";
 import type { LocalVideoTrack, Room, VideoSource } from "@livekit/rtc-node";
+import { config } from "../config.js";
 import { logger } from "../logger.js";
 
 // revoice.js pulls in the CommonJS build of @livekit/rtc-node, and the native
@@ -49,10 +50,13 @@ export class VideoPublisher {
   async start(room: Room, stream: Readable, onGiveUp?: (reason: string) => void): Promise<void> {
     const { width, height } = this.options;
     const source = new rtc.VideoSource(width, height);
-    const track = rtc.LocalVideoTrack.createVideoTrack("screen", source);
+    // As a camera the picture appears inside the bot's own tile; a screen share
+    // is rendered as a separate tile by every client.
+    const asScreen = config.VIDEO_SOURCE === "screen";
+    const track = rtc.LocalVideoTrack.createVideoTrack(asScreen ? "screen" : "video", source);
 
     const options = new rtc.TrackPublishOptions();
-    options.source = rtc.TrackSource.SOURCE_SCREENSHARE;
+    options.source = asScreen ? rtc.TrackSource.SOURCE_SCREENSHARE : rtc.TrackSource.SOURCE_CAMERA;
 
     const participant = room.localParticipant;
     if (!participant) throw new Error("room has no local participant yet");
@@ -75,7 +79,10 @@ export class VideoPublisher {
     }, FIRST_FRAME_TIMEOUT_MS);
     this.firstFrameTimer.unref?.();
 
-    log.info({ width, height, sid: publication.sid }, "screen share published");
+    log.info(
+      { width, height, source: config.VIDEO_SOURCE, sid: publication.sid },
+      "video track published",
+    );
   }
 
   private consume(chunk: Buffer): void {