The shim's permissions (devices=all, its store path, LD_PRELOAD,
SFN_MPV_HWDEC) were a Flatpak override: through nix-flatpak's
services.flatpak.overrides, whose override file outlives the
configuration (it left an empty file behind), or a Home Manager link that
`flatpak override --user` would replace (hence `force`). Now a desktop
entry shadowing the Flatpak's (same ID, same fields and actions; also what
the "+" menu sees) passes them as `flatpak run` options
(--device=all --filesystem=<shim>:ro --env=...), so nothing is written to
Flatpak's overrides and they disappear with the entry.
jellyfin.hardwareDecoding.command is that command line for a terminal.
The entries earlier versions put into the override file are removed by
steam-frame-nix-cleanup. Checked with `flatpak run ... --command=sh`: the
shim's store path is visible read-only, the environment is set and
/dev/video* is there.
Every module imports cleanup.nix (also exported as
homeManagerModules.cleanup), which
- puts steam-frame-nix-cleanup (install.sh cleanup) on PATH;
- runs `cleanup --orphans --quiet` after linkGeneration on every switch,
keeping what the configuration still uses (steamFrame.cleanup.keep, set
by the modules: debugger while steamvrDebugger is on, the Firefox desktop
profile's user.js while its fix applies); in a dry run it runs with
--dry-run;
- runs `cleanup --all` instead when Home Manager's `uninstall = true;` is
set (the manual uninstall route);
- removes links of older versions at paths Home Manager is about to own
before checkLinkTargets (steamFrame.cleanup.migrateLinks), which would
count as collisions otherwise.
install.sh cleanup gains --quiet (only actions, deferrals and warnings;
the header only when something is printed). The Jellyfin module's own
removal of the old shim copy goes: cleanup does it.
Jellyfin Desktop hard-sets mpv's hwdec=auto-copy, whose probe list leaves
out V4L2 M2M, and the Flatpak can't see the Frame's V4L2 decoder. An
LD_PRELOAD shim (preloaded straight from the store, only that path exposed
read-only) rewrites hwdec to v4l2m2m-copy,auto-copy; devices=all makes the
decoder visible. Overrides via nix-flatpak, or a home-manager-owned override
file without it.
Pierre Kisters