The mpv service inherited Kodi's VT-grabbing block (PAMName=login +
StandardInput=tty + TTYPath=/dev/tty1). Opening a "login" PAM session on
tty1 hangs in systemd's pre-exec setup, so mpv was never exec'd at all --
the service sat "running" as systemd-executor with an empty (mpv) cmdline,
no IPC socket, no output.
Two fixes:
1. Simplify the unit. mpv doesn't need a login session or the tty: as the
sole DRM client on the seat it becomes DRM master implicitly on first
open, so plain video+render+audio group membership is enough. Removing
the PAM/tty block lets mpv actually start, initialize the vc4 KMS
display, and play (verified end-to-end: play/status/next through the
Flask API, position advancing on screen).
2. install.sh now tears down any leftover Kodi before starting mpv. The
real trigger this time was an in-place migration: replacing the unit
files doesn't stop an already-running Kodi, which kept DRM master and
the tty1 seat and blocked mpv from ever getting the display.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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