fill-music-player

name	fill-music-player
description	Use when a user wants to fill a portable music player (Walkman, iPod, USB drive) with a curated random selection from a music library on a NAS or local directory. Handles format filtering, artist/album diversity balancing, and size targeting.
license	MIT
allowed-tools	Bash
compatibility	Codex, Claude Code, Cursor, GitHub Copilot, Windsurf, Kiro, and other Agent Skills compatible tools. Requires shell access and the fill-music-player CLI or underlying script in the target environment.
metadata	{"targets":["_source-only"],"author":"Oleg Koval","tags":["music","media","curation","copy","cli"]}

fill-music-player

Curates a DJ-balanced selection of tracks from a source music library and copies them to a portable player, respecting device capacity and supported formats.

Quick Reference

# Dry run first (always recommend this)
fill-music-player --source /Volumes/music --dest /Volumes/WALKMAN/MUSIC --dry-run

# Copy for real
fill-music-player --source /Volumes/music --dest /Volumes/WALKMAN/MUSIC

# Or run the script directly with uv
uv run fill_music_player.py --source ~/Music --dest /Volumes/USB --dry-run

Run fill-music-player --help for all options.

Key Parameters

Flag	Default	Purpose
--source / -s	required	Source music root (NAS mount, ~/Music, etc.)
--dest / -d	required	Player destination directory
--target-gb	95% of free space	How many GB to fill
--formats	mp3,m4a,wma,aac	Allowed extensions
--max-per-artist	4	Artist diversity cap
--max-per-album	3	Album diversity cap
--skip-dirs	(none)	Top-level dirs to skip
--dry-run	false	Preview without copying

Workflow

1. Always do --dry-run first
2. Review the per-genre breakdown
3. Adjust --skip-dirs, --max-file-mb, or --max-per-artist if needed
4. Run without --dry-run to copy

Device Formats

Device	Recommended --formats
Sony Walkman NWZ series	mp3,m4a,wma
iPod (classic/nano)	mp3,m4a,aac
Generic USB player	mp3
Any modern player	mp3,m4a,wma,aac,ogg,flac

Edge Cases and Troubleshooting

Situation	What happens	Fix
NAS disconnects mid-copy	Copy fails for that file, logged as error, continues with next track	Re-run; already-copied files are skipped (if not dst.exists())
Source has only FLAC/lossless	0 files selected (FLAC not in default formats)	Use --formats flac or --formats mp3,flac
FAT32 filename too long or illegal chars	Filenames are sanitized: <>:"/|?* replaced with _, truncated to 80 chars	Automatic — no action needed
Mixed/broken ID3 tags	Falls back to folder name parsing (Genre/Artist - Album/track.mp3)	Works transparently; folder structure is the reliable fallback
Very large files (DJ mixes, radio shows)	Skipped by default (>20 MB)	Adjust with --max-file-mb 50 to include mixes
Tiny files (jingles, corrupt)	Skipped by default (<300 KB)	Adjust with --min-file-kb 100 to be more permissive
One artist dominates the library	Capped at 4 tracks per artist, 3 per album	Lower with --max-per-artist 2 for more variety
Empty genre directories	Silently skipped, no error	Normal behavior
Destination already has files	Existing files are not overwritten or deleted; new tracks added alongside	Clear destination first if you want a fresh set
SMB/NFS mount is slow	Scanning with mutagen tag reading can take 5-10 min for large libraries	Expected; the dry-run output appears once scanning completes

Real-World Example

Filling a Sony Walkman NWZ-B183F (4 GB) from a Synology DS918+ NAS with ~9,000 tracks across blues, funk, hip-hop, soul, IDM, dubstep, dub, indie, and post-rock:

# Step 1: Preview
fill-music-player \
  --source /Volumes/music \
  --dest /Volumes/WALKMAN/MUSIC \
  --skip-dirs "jingles,!recordings,!restored,dubrecords" \
  --formats mp3,m4a,wma \
  --dry-run

# Output:
#   Found 8914 candidate tracks across 14 genres
#   Funk     →  86 tracks  (440.8 MB)
#   blues    →  38 tracks  (316.7 MB)
#   hiphop   →  33 tracks  (234.7 MB)
#   ...
#   Selected 348 tracks  (2473.0 MB)

# Step 2: Copy
fill-music-player \
  --source /Volumes/music \
  --dest /Volumes/WALKMAN/MUSIC \
  --skip-dirs "jingles,!recordings,!restored,dubrecords" \
  --formats mp3,m4a,wma

Result: 348 tracks, 2.4 GB, balanced across 14 genres with max 4 tracks per artist. Artists included Fela Kuti, ZZ Top, Mobb Deep, Gregory Porter, Tinariwen, Chick Corea, Hudson Mohawke, and Funkadelic. Total copy time over SMB: ~12 minutes.