feat: recording playback speed control

[dwmkerr]

Summary

Add a playbackSpeed option to control the pace of GIF recordings (e.g., 1.5x, 2x). This would eliminate frames before deduplication to create faster-paced recordings.

Use Case

Long recordings with lots of idle time can be compressed via frame deduplication, but the actual pace remains 1:1 with real-time. A playback speed option would allow creating snappier demos without manually editing.

Proposed Approach

Add playbackSpeed parameter to shell_record_stop:

• 1.0 = normal speed (default)
• 1.5 = 50% faster
• 2.0 = double speed

Implementation: reduce frame delays by the speed factor before deduplication. For example, at 2x speed, a 100ms delay becomes 50ms.

Example

{
  "session_id": "shell-session-abc",
  "name": "demo",
  "playbackSpeed": 1.5
}

Notes

• Should be applied before frame deduplication for best results
• Could also be a render-time option in renderGif()