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 #

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 #

1. tape-to-mp4.mjs (line 92)

   • Added scale filter to ffmpeg arguments

2. media-atproto.mjs (lines 167-215)

   • TAPE buildRecord with MP4 conversion
   • Dynamic import of tape-to-mp4.mjs
   • Blob upload logic

3. sync-atproto.mjs

   • Added --tapes-only flag
   • Anonymous content support

Next Steps #

1. ✅ Test complete - all 32 anonymous tapes synced
2. 🔄 Sync Jeffrey's content (~3,000 items)
3. 🔄 Deploy to production
4. 🔄 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 ✅