Add compressed sample video and extracted audio track

Replaces the 418 MB 1080p source video with a 27 MB 480p derivative and
adds the audio track extracted losslessly from it (AAC stream copy, no
re-encode), which is what the whisperx/demucs/tts demos actually consume.

The full-size source is now gitignored and kept locally only, matching
the existing convention of excluding large binaries from the repo.

Co-Authored-By: Claude Opus 5 <[email protected]>

.gitignore

@@ -25,3 +25,7 @@ outputs/
 .DS_Store
 .idea/
 .vscode/
+
+# Full-size source video — keep locally, commit only compressed derivatives
+media-files/video/*.mp4
+!media-files/video/*-480p.mp4