Tape MP4 Conversion - Success Report#

Summary#

Successfully implemented and tested MP4 video conversion for aesthetic.computer tapes with ATProto blob uploads.

Problem Solved#

H.264 encoding requires video dimensions divisible by 2. Many tapes have odd-width canvases (e.g., 337x160).

Solution#

Added ffmpeg scale filter: scale=trunc(iw/2)*2:trunc(ih/2)*2

Rounds down to nearest even number
Preserves aspect ratio
Minimal quality impact (1px maximum width/height adjustment)

Test Results#

Date: 2025-01-25 Test Set: 32 anonymous tapes from art.at.aesthetic.computer

Metrics#

✅ 100% success rate (32/32 conversions)
✅ MP4 sizes: 27.71 KB - 439.04 KB (average ~180 KB)
✅ Frame rate: 60 fps (calculated from timing.json)
✅ Codec: H.264 with yuv420p pixel format
✅ Optimization: faststart flag enabled for web streaming
✅ All blobs uploaded to ATProto successfully
✅ All MongoDB records updated with rkeys

Sample Conversions#

Tape Code	ZIP Size	MP4 Size	Dimensions
9Yo	Unknown	108.89 KB	640x480 (even)
eKZ	Unknown	343.71 KB	337x176 → 336x176
3Pt	Unknown	27.71 KB	Small tape
oSm	Unknown	439.04 KB	Longest tape

Implementation Details#

ffmpeg Arguments#

-r 60                                      # Frame rate (from timing.json)
-i /tmp/tape-xxx/frame-%05d.png           # Input frames (5-digit padded)
-vf scale=trunc(iw/2)*2:trunc(ih/2)*2     # Ensure even dimensions
-c:v libx264                               # H.264 codec
-pix_fmt yuv420p                           # Compatible pixel format
-movflags +faststart                       # Web streaming optimization
-y output.mp4                              # Overwrite output

Error Handling#

Falls back to no blob if conversion fails
Record still created with zipUrl and acUrl
Cleanup of temp directories guaranteed

Files Modified#

tape-to-mp4.mjs (line 92)
- Added scale filter to ffmpeg arguments
media-atproto.mjs (lines 167-215)
- TAPE buildRecord with MP4 conversion
- Dynamic import of tape-to-mp4.mjs
- Blob upload logic
sync-atproto.mjs
- Added --tapes-only flag
- Anonymous content support

Next Steps#

✅ Test complete - all 32 anonymous tapes synced
🔄 Sync Jeffrey's content (~3,000 items)
🔄 Deploy to production
🔄 Full sync of 4,201 users

Performance Notes#

Conversion time: ~3-5 seconds per tape
Batch size: 10 concurrent conversions
Total time for 32 tapes: ~2 minutes
No rate limiting issues with ATProto blob uploads

Storage Impact#

Average MP4 size: ~180 KB
32 tapes: ~5.76 MB total
Extrapolated for all users: Estimated 50-100 MB (assuming ~300-500 tapes total)

Conclusion#

MP4 conversion implementation is production-ready ✅

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