feat: mpv config from various scripts

mpv/scripts/mpv-gnome-inhibit.lua

@@ -0,0 +1,131 @@
+--[[
+
+Prevent the screen from blanking while a video is playing.
+
+This script is a workaround for the GNOME+Wayland issue documented in the
+[Disabling Screensaver] section of the mpv manual, and depends on
+gnome-session-inhibit (usually provided by the gnome-session package) to set up
+the inhibitors.
+
+
+# CAVEATS
+
+This is not (yet?) a foolproof solution.
+
+At this time GNOME's implementation of the Inhibit protocol does not support the
+SimluateUserActivity method:
+
+    dbus-send --print-reply --session \
+      --dest=org.gnome.ScreenSaver --type=method_call \
+      /org/gnome/ScreenSaver org.gnome.ScreenSaver.SimulateUserActivity
+
+So there seems to be no way to "poke" the system with a heartbeat to extend to
+idle timeout for a bit and prevent blanking.
+
+This means that inhibitors have to be installed, then removed when mpv exits.
+
+The current implementation handles this via another application, which should
+alwasy be available on GNOME+Wayland desktops (because provided by gnome-session
+itself): gnome-session-inhibit.
+
+Executing gnome-session-inhibit to handle this is not ideal because if mpv does
+not exit cleanly, gnome-session-inhibit is not necessarily killed (it can get
+ophaned, and gets adopted by the init process), leaving the inhibitors intact
+with no easy way for the user to figure it out.
+
+Ideally this script should open a DBus session directly to handle the
+inhibitors, as they would be removed if the DBus session gets disconnected (cf.
+[Inhibit's documentation][Inhibit]):
+
+> Applications should invoke [Inhibit ()] when they begin an operation that
+> should not be interrupted [...] When the application completes the operation
+> it should call Uninhibit() or disconnect from the session bus.
+
+This is how [other applications] do it.
+
+But really, the only secure way to handle this would be with a heartbeat to
+regularly reset the idle timer, i.e. what SimulateUserActivity is supposed to
+provide. Especially for a core security feature such as screen locking (cf.
+xscreensaver's author [rant][jwz]).
+
+
+# TODO
+
+- Do not inhibit for audio-only playback, only for video
+- Fix inhibitors not removed when mpv does not terminate gracefully, e.g. with
+  `kill -9 <pid>`, either by having a wrapper around gnome-session-inhibit
+  checking the parent PID (see https://stackoverflow.com/a/2035683), or by
+  interfacing with dbus to open a session that gets disconnected if mpv
+  terminates uncleanly (hopefully), or ...
+- Investigate whether the 'playback-abort' event should be handled
+- Only inhibit when the player is visible
+
+
+[Disabling Screensaver]: https://mpv.io/manual/master/#disabling-screensaver
+[Inhibit]: https://people.gnome.org/~mccann/gnome-session/docs/gnome-session.html#org.gnome.SessionManager.Inhibit
+[jwz]: https://www.jwz.org/blog/2021/01/i-told-you-so-2021-edition/
+[other applications]: https://unix.stackexchange.com/a/438335
+
+]]
+
+
+local mp = require 'mp'
+local msg = require 'mp.msg'
+
+local cookie
+
+local function handle_inhibit(_, paused)
+    if paused and cookie then
+        mp.abort_async_command(cookie)
+        cookie = nil
+        msg.debug('inhibit off')
+    elseif not paused and not cookie then
+        cookie = mp.command_native_async(
+            {
+                name = 'subprocess',
+                args = {
+                    'gnome-session-inhibit',
+                    '--inhibit-only',
+                    '--inhibit', 'idle',
+                    '--app-id', 'mpv',
+                    '--reason', 'video-playing',
+                },
+
+                -- `playback_only = true` does not kill the command when
+                -- playback is paused (i.e. "pause" is still "playback == true")
+                -- but also kills it immediately the first time.
+                -- So we need to handle the paused state ourselves.
+                playback_only = false,
+
+                -- If not captured, mpv will just forward everything to stdout
+                -- and stderr. Setting capture_stdXXX with capture_size = 0 will
+                -- ensure that the command's output is discarded.
+                capture_stdout = true,
+                capture_stderr = true,
+                capture_size = 0,
+            },
+
+            -- Should be optional according to the doc, but I get an error if I
+            -- don't provide a function: attempt to call local 'cb' (a nil value)
+            function() end
+        )
+
+        msg.debug('inhibit on')
+    end
+end
+
+mp.observe_property('stop-screensaver', 'bool', function(_, enable)
+    if enable then
+        mp.observe_property('pause', 'bool', handle_inhibit)
+        msg.debug('inhibit handling on')
+    else
+        mp.unobserve_property('pause', 'bool', handle_inhibit)
+        msg.debug('inhibit handling off')
+
+        if cookie then
+            mp.abort_async_command(cookie)
+            cookie = nil
+            msg.debug('inhibit off')
+        end
+    end
+end)