autosave.lua

-- autosave.lua
--
-- Periodically saves "watch later" data during playback, rather than only saving on quit.
-- This lets you easily recover your position in the case of an ungraceful shutdown of mpv (crash, power failure, etc.).
--
-- You can configure the save period by creating a "lua-settings" directory inside your mpv configuration directory.
-- Inside the "lua-settings" directory, create a file named "autosave.conf".
-- The save period can be set like so:
--
-- save_period=60
--
-- This will set the save period to once every 60 seconds of playback, time while paused is not counted towards the save period timer.
-- The default save period is 30 seconds.
local options = require 'mp.options'

local o = {
	save_period = 30
}

options.read_options(o)

local mp = require 'mp'

local function save()
	mp.commandv("set", "msg-level", "cplayer=warn")
	mp.command("write-watch-later-config")
	mp.commandv("set", "msg-level", "cplayer=status")
end

local save_period_timer = mp.add_periodic_timer(o.save_period, save)

local function pause(name, paused)
	save()
	if paused then
		save_period_timer:stop()
	else
		save_period_timer:resume()
	end
end

mp.observe_property("pause", "bool", pause)
mp.register_event("file-loaded", save)

local function end_file(data)
	if data.reason == 'eof' or data.reason == 'stop' then
		local playlist = mp.get_property_native('playlist')
		for i, entry in pairs(playlist) do
			if entry.id == data.playlist_entry_id then
				mp.commandv("delete-watch-later-config", entry.filename)
				return
			end
		end
	end
end
mp.register_event("end-file", end_file)

Yeah, I think it reads the file with the same parser as for mpv.conf, which doesn't seem to support things like lists.

Your fork doesn't work for me, and it even makes the default write-watch-later-config command to not work. I tried the original one and TheDrHax's forks and they worked.

Windows 10 21H2 19044.2251
mpv 0.35.0-30-g4574dd5dc6

I'm not sure why it doesn't work for you. Note that the critical difference of this fork vs. other versions is supporting playlists - we need to delete the watch_later bookmark when leaving one file and before going to the next one, otherwise resuming playback of the playlist will not work.

@CyberShadow does it also save when the video paused? if it does it would be perfect!

Yes, you can see it calls save() in the pause function.