Uploaded videos carry no dimensions, so a vertical clip sat letterboxed in a 16:9 frame. The player now takes the frame size from the file's metadata when the block has none. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MRtGG9ARfqqhma3t85Ro2u