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GROK BOT / encode-still-cover-video-for-quicktime-chat

Grok Bot

Encode a still-cover track that QuickTime plays under the chat video limit

encode-still-cover-video-for-quicktime-chat

When Grok Bot builds a review video from a still image plus a full-length audio track, two limits show up together: chat delivery caps video around 200 MB, and a still encoded at 1 fps with AAC often goes silent mid-track in QuickTime. Cursor staff (deanrie, thread 172600) documented both the limit and a working encode path.

What fails

  • ProRes + PCM (or similar lossless pairs) for a full track often lands near multi-GB on the agent computer. Chat will not take that file. CopyFromBox is for small files. Drive and Dropbox connectors do not accept a large binary upload yet.
  • A still at ~1 fps plus AAC in a .mov can play with a silent gap in the middle of the track in QuickTime, even when the file is under the chat cap.

Staff’s note: raising handoff limits and adding a proper binary upload path are tracked product requests. Until those ship, encode for the limits that exist today.

Encode for QuickTime and the chat cap

Ask the Bot (or run on the agent computer) for an H.264 still cover at a normal frame rate, ALAC audio, .mov container:

ffmpeg -loop 1 -framerate 24 -i cover.png -i track.wav \
  -c:v libx264 -tune stillimage -pix_fmt yuv420p -r 24 \
  -c:a alac \
  -shortest -movflags +faststart \
  out.mov

Two settings matter for QuickTime:

  1. Frame rate 24 or 30 (not 1 fps).
  2. Pixel format yuv420p.

ALAC stays lossless like PCM for the audio while staying much smaller than ProRes+PCM, so a full-length still-cover track usually fits under the ~200 MB chat video limit and can be sent in chat.

If you specifically need AAC, keep the same frame-rate and yuv420p fixes and add -ar 48000. Staff reported that combination usually clears the mid-track drop.

Delivery order

  1. Build out.mov with the command above on the agent computer.
  2. Confirm size is under ~200 MB (ls -lh out.mov).
  3. Attach or send the file through chat.
  4. Open it in QuickTime and scrub past the middle of the track to confirm audio stays present.

If ALAC still goes silent in QuickTime, send staff the exact ffmpeg command and the file duration on the forum thread.

Pitfalls

  • Do not Reset or rebuild the agent computer to “fix” a stuck multi-GB encode. The file is over the delivery limit.
  • CopyFromBox will not move multi-GB review masters to your Mac.
  • Leaving -r 1 or omitting yuv420p recreates the QuickTime silence even when size looks fine.

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