Loom Capture Pipeline - Validation Report

Loom Capture Pipeline - Validation Report

Date: 2026-02-10 System: macOS Darwin 25.2.0, Apple Silicon (ARM64) ffmpeg: 8.0.1 (Homebrew, with libx264/libx265/videotoolbox/audiotoolbox)

Test Results Summary

Overall: 6/9 PASS, 0 FAIL (functional), 3 SKIP (Chrome MCP dependency)

Test Details

Test 1: Dependencies

which ffmpeg && ffmpeg -version | head -1
# /opt/homebrew/bin/ffmpeg
# ffmpeg version 8.0.1 Copyright (c) 2000-2025 the FFmpeg developers

which osascript
# /usr/bin/osascript

Encoders confirmed: libx264, libx265, libmp3lame, libopus, libvpx, libwebp, videotoolbox, audiotoolbox.

Test 2: Chrome MCP

mcp__claude-in-chrome__tabs_context_mcp -> "No Chrome extension connected."

Chrome MCP requires launching Claude Code with claude --chrome flag. The extension must be installed and Chrome running. This is an environment requirement, not a code issue.

Test 3: Chrome Window Bounds

osascript -e 'tell application "Google Chrome" to get bounds of window 1'
# 0, 33, 1512, 915

• Window position: (0, 33) top-left
• Window size: 1512x882 (usable area)
• Note: Native Retina resolution is 3024x1964 (2x scaling)

Test 4: ffmpeg avfoundation Screen Capture

ffmpeg -y -f avfoundation -framerate 30 \
  -capture_cursor 1 -capture_mouse_clicks 1 \
  -i "2:none" \
  -t 5 \
  -c:v libx264 -preset ultrafast -crf 18 \
  /tmp/loom-test/screen-test.mp4

Output:

• Resolution: 3024x1964 (native Retina)
• Frame rate: 30 fps
• Codec: h264 (libx264)
• Duration: 4.97s
• File size: 1.97 MB
• Bitrate: ~3226 kbps

Key Notes:

• Screen device index is 2 ("Capture screen 0")
• Audio device "none" disables audio capture
• -capture_cursor 1 -capture_mouse_clicks 1 captures mouse interactions
• ffmpeg auto-overrides pixel format to uyvy422 (avfoundation limitation)
• NSKVONotifying_AVCaptureScreenInput warnings are cosmetic, non-fatal

Test 5: macOS screencapture (Fallback)

screencapture -v -V 5 /tmp/loom-test/screencapture-test.mov

Output:

• Resolution: 3024x1964 (native Retina)
• Frame rate: 120 fps (!)
• Codec: h264
• Duration: 5.03s
• File size: 9.69 MB
• Container: MOV

Comparison vs ffmpeg:

• screencapture captures at 120fps (5x more than needed), producing 5x larger files
• ffmpeg gives precise control over fps, codec, CRF, and resolution
• Recommendation: Use ffmpeg as primary, screencapture as emergency fallback

Test 7: Combined Background Capture + Automation

# Start recording in background
ffmpeg -y -f avfoundation -framerate 30 \
  -capture_cursor 1 -capture_mouse_clicks 1 \
  -i "2:none" -t 5 \
  -c:v libx264 -preset ultrafast -crf 18 \
  -pix_fmt yuv420p -s 1280x720 \
  /tmp/loom-test/combined-test.mp4 &
FFMPEG_PID=$!

# Perform actions during recording
sleep 1
osascript -e 'tell application "Google Chrome" to set URL of active tab of window 1 to "https://example.com"'
sleep 2
osascript -e 'tell application "System Events" to key code 125 using {command down}'
sleep 2

wait $FFMPEG_PID

Output:

• Resolution: 1280x720 (scaled from native)
• Frame rate: 30 fps
• Codec: h264 (libx264)
• Duration: 4.97s
• File size: 2.59 MB
• Bitrate: ~4369 kbps (more activity = slightly higher bitrate)

Key Finding: Background ffmpeg + foreground osascript automation works correctly. The pipeline can record while orchestrating Chrome navigation.

Test 9: FFmpeg Assembly Pipeline

9a: Title Card Generation

ffmpeg -y -f lavfi -i "color=c=0x1a1a2e:s=1280x720:d=3" \
  -vf "drawtext=text='Test Title':fontcolor=white:fontsize=48:x=(w-text_w)/2:y=(h-text_h)/2" \
  -c:v libx264 -crf 20 /tmp/loom-test/title-test.mp4

• Output: 7.4 KB, 1280x720, 3 seconds, 25fps
• drawtext filter works with default font

9b: Silent Audio Track

ffmpeg -y -f lavfi -i "anullsrc=r=44100:cl=mono" -t 5 -c:a libmp3lame /tmp/loom-test/silence.mp3

• Output: 40 KB, 5 seconds, 44100 Hz mono

9c: Video Concatenation

printf "file '/tmp/loom-test/title-test.mp4'\n" > /tmp/loom-test/concat.txt
echo "file '/tmp/loom-test/title-test.mp4'" >> /tmp/loom-test/concat.txt
ffmpeg -y -f concat -safe 0 -i /tmp/loom-test/concat.txt -c copy /tmp/loom-test/concat-test.mp4

• Output: 14 KB, 6.0 seconds (2 x 3s clips concatenated)
• Concat demuxer works with -c copy (no re-encoding)

Video Specs Achieved

Recommended Capture Method

Primary: ffmpeg avfoundation (Test 4)

ffmpeg -y -f avfoundation -framerate 30 \
  -capture_cursor 1 -capture_mouse_clicks 1 \
  -i "2:none" \
  -t <DURATION> \
  -c:v libx264 -preset ultrafast -crf 18 \
  -pix_fmt yuv420p -s 1280x720 \
  <OUTPUT>.mp4

Advantages:

• Full control over resolution, fps, codec, quality
• Can scale on-the-fly (native 3024x1964 -> 1280x720)
• Smaller files than screencapture
• Can run in background while osascript drives Chrome
• -t flag provides reliable duration control

Fallback: macOS screencapture (Test 5)

screencapture -v -V <DURATION> <OUTPUT>.mov

Use only if ffmpeg avfoundation fails or Screen Recording permission is revoked.

Issues and Workarounds

1. No timeout command on macOS

• macOS does not ship GNU timeout
• Workaround: Use ffmpeg's -t flag for duration control, or install coreutils (brew install coreutils for gtimeout)

2. Pixel format override warning

• ffmpeg warns: "Selected pixel format (yuv420p) is not supported by the input device"
• Automatically overrides to uyvy422 for capture, then converts to yuv420p for output
• No action needed — this is expected behavior

3. Chrome MCP requires --chrome flag

• claude --chrome must be used to enable Chrome browser tools
• Chrome extension must be installed and Chrome running
• Impact: Tests 6, 8 (Chrome automation, GIF creator) could not be validated
• Workaround for automation: osascript can drive Chrome navigation, scrolling, and window management as demonstrated in Test 7

4. NSKVONotifying warnings

• objc: class 'NSKVONotifying_AVCaptureScreenInput' not linked into application
• Cosmetic ObjC runtime warning, does not affect capture
• No action needed

Screen Recording Permission Status

GRANTED — Both ffmpeg avfoundation and macOS screencapture successfully recorded the screen. This confirms that the terminal/Claude Code process has Screen Recording permission in System Settings > Privacy & Security > Screen Recording.

Chrome MCP Status

To enable Chrome MCP: Relaunch with claude --chrome

Generated Test Artifacts