Hacky demo changes

video/src/video.ts

@@ -0,0 +1,58 @@
+import { execSync } from 'node:child_process';
+import { renameSync, statSync } from 'node:fs';
+import {
+  MAX_DURATION_S,
+  OUTPUT_FPS,
+  RECORD_SCALE,
+  VIDEO_SIZE,
+  WEBM_BITRATE,
+} from './config.js';
+
+const LEAD_IN_S = 0.12;
+
+export function trimRecording(
+  rawPath: string,
+  trimmedPath: string,
+  times: { recordStartMs: number; sceneStartMs: number; sceneEndMs: number }
+) {
+  const sceneSpan = (times.sceneEndMs - times.sceneStartMs) / 1000;
+  const trimStart = Math.max(
+    0,
+    (times.sceneStartMs - times.recordStartMs) / 1000 - LEAD_IN_S * RECORD_SCALE
+  );
+  const trimEnd = (times.sceneEndMs - times.recordStartMs) / 1000;
+  const wallDuration = trimEnd - trimStart;
+  const finalDuration = wallDuration / RECORD_SCALE;
+
+  if (finalDuration > MAX_DURATION_S) {
+    console.log(
+      `Scene output duration is ${finalDuration.toFixed(2)}s (guard ${MAX_DURATION_S.toFixed(2)}s); keeping the full take.`
+    );
+  }
+
+  const filter =
+    `trim=start=${trimStart.toFixed(3)}:duration=${wallDuration.toFixed(3)},` +
+    `setpts=(PTS-STARTPTS)/${RECORD_SCALE},fps=${OUTPUT_FPS},` +
+    `trim=duration=${finalDuration.toFixed(3)},setpts=PTS-STARTPTS`;
+
+  // Keep trimming inside the filter graph: it is frame-accurate for WebM
+  // without the keyframe leakage of input seeking or the post-speedup timing
+  // ambiguity of output seeking.
+  execSync(
+    `ffmpeg -y -i "${rawPath}" -vf "${filter}" ` +
+      `-fps_mode cfr -r ${OUTPUT_FPS} -c:v libvpx -b:v ${WEBM_BITRATE} -deadline good -cpu-used 5 ` +
+      `"${trimmedPath}"`,
+    { stdio: 'inherit' }
+  );
+
+  try {
+    statSync(rawPath);
+    renameSync(rawPath, rawPath + '.untrimmed');
+  } catch {
+    /* ignore */
+  }
+
+  console.log(
+    `Wrote ${trimmedPath} (${finalDuration.toFixed(2)}s, scene=${(sceneSpan / RECORD_SCALE).toFixed(2)}s, scale=${RECORD_SCALE}, capture=${VIDEO_SIZE.width}x${VIDEO_SIZE.height})`
+  );
+}