Running Sonic/Loudness Analysis on ephemeral cloud instance - API or CLI approach?

Dev Community Dev/API Corner
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Hello,

I’m spinning up temporary Plex servers in the cloud to scan my 9TB library, then exporting the database back to my low-power zimaboard which is too slow for initial library scanning (especially Sonic analysis on 7TB of music).

Discovery works great, but deep analysis like sonic analysis never runs.

Looking for the correct API/CLI method to trigger it programmatically.

Environment

  • Plex Docker: plexinc/pms-docker:latest
  • OS: Ubuntu
  • Storage: S3 via rclone mount (vfs-cache-mode full)
  • Plex Pass: Lifetime (verified active)

What Works

  • Instance provisioning (Docker)
  • S3 mounting via rclone
  • Plex container with valid claim token
  • Plex Pass is active (verified via /myplex/account then subscriptionActive=\"1\")
  • Library creation via API
  • Discovery phase : example for a part of the music library : 2114 tracks found, 172 bundles (artists + albums) created

What Doesn’t Work

Sonic/Loudness analysis: 0% completion

After discovery, I trigger analysis via:

# Method 1: API
curl -X PUT \"http://localhost:32400/library/sections/1/analyze?force=1\" \\
  -H \"X-Plex-Token: $TOKEN\"

# or Method 2: CLI
# --server-action sonic seems ignored
docker exec plex '/usr/lib/plexmediaserver/Plex Media Scanner' \\
  --analyze --section 1 --server-action sonic

Both return successfully, but checking the database shows no tracks have ms:musicAnalysisVersion in extra_data:

SELECT COUNT(*) FROM metadata_items 
WHERE metadata_type = 10 
AND extra_data LIKE '%ms:musicAnalysisVersion%';
-- Result: 0

Additional informations

  • CPU stays low (~2-5%) during "analysis" phase
  • No Sonic or Loudness entries in Scanner logs
  • The server is claimed and Plex Pass is active
  • Preferences like LoudnessAnalysis don’t seem to exist in /:/prefs

Questions

  1. Is there a specific API endpoint or CLI flag to force Sonic analysis?
  2. Does Sonic analysis require the server to be "settled" for some time?
  3. Is there a preference I need to enable first?

Any help in automating the Plex scan or initiating the Sonic scan via API or CLI would be greatly appreciated.

Thanks in advance