docs: update mining demo and scale video crops

- Refresh mining demo assets and documentation references
- Scale mpv crop coordinates for resized OBS recordings

scripts/mkv-to-readme-video.sh

@@ -19,7 +19,8 @@ Options:
   -w, --webp   Generate animated WebP preview
 
 Encoding profile:
-  - Crop: 1920x1080 at x=760 y=200
+  - Crop: mpv region at 1920x1080, x=760 y=205 on a 3440x1440 canvas
+  - Output size: 1920x1080
   - MP4:  H.264 + AAC
   - WebM: AV1/VP9 + Opus at 30 fps
 USAGE
@@ -148,7 +149,8 @@ pick_webp_encoder() {
 	return 1
 }
 
-crop_vf="crop=1920:1080:760:205"
+# OBS may resize the 3440x1440 canvas, so scale the mpv bounds with the input.
+crop_vf="crop=1920*iw/3440:1080*ih/1440:760*iw/3440:205*ih/1440,scale=1920:1080:flags=lanczos"
 webm_vf="${crop_vf},fps=30"
 
 echo "Generating MP4: $mp4_out"

scripts/mkv-to-readme-video.test.ts

@@ -40,7 +40,7 @@ function toBashPath(filePath: string): string {
   return `${drive.toUpperCase()}:/${rest}`;
 }
 
-test('mkv-to-readme-video accepts libwebp_anim when libwebp is unavailable', () => {
+test('mkv-to-readme-video builds every output with the scaled mpv crop', () => {
   withTempDir((root) => {
     const binDir = path.join(root, 'bin');
     const inputPath = path.join(root, 'sample.mkv');
@@ -104,5 +104,9 @@ touch "$output"
 
     const ffmpegLog = fs.readFileSync(ffmpegLogPath, 'utf8');
     assert.match(ffmpegLog, /-c:v libwebp_anim/);
+    const scaledCropUses = ffmpegLog.match(
+      /-vf crop=1920\*iw\/3440:1080\*ih\/1440:760\*iw\/3440:205\*ih\/1440,scale=1920:1080:flags=lanczos/g,
+    );
+    assert.equal(scaledCropUses?.length, 4);
   });
 });