MPV script that fixes video sync on some broken videos where both the audio and video PTS are incorrect by a constant factor. This is appearent on some videos exported from Topaz VEAI from the looks of it. This essentially works by measuring how much frames drop due to display sync and calculating the correct video fps and changes it via the set…

fix-sync.lua

local mp = require 'mp'

function fix_sync()
	-- Capture the first snapshot
	local start_dropped = mp.get_property_number("mistimed-frame-count") or 0
	local fps = mp.get_property_number("container-fps") or 0
	if fps == 0 then return end

	mp.add_timeout(1, function()
		-- Capture the second snapshot
		local end_dropped = mp.get_property_number("mistimed-frame-count") or 0
		local drops_per_second = end_dropped - start_dropped
		local dps_threshold = fps * 0.5

		-- If no significant portion of frames were dropped, no need to adjust
		if drops_per_second <= dps_threshold then
			return
		end

		local override_fps = fps + drops_per_second
		local raw_multiplier = fps / override_fps
		local pts_multiplier = math.floor(raw_multiplier * 10 + 0.5) / 10

		-- Apply settings to compensate for drop rate
		mp.commandv("vf", "add", "@sync:setpts=".. pts_multiplier .."*PTS")
		mp.commandv("af", "add", "@sync:asetpts=" .. pts_multiplier .. "*PTS")

		mp.msg.info("Sync fix applied: A/V PTS multiplier set to " .. pts_multiplier)
	end)
end

mp.register_event("file-loaded", function()
	-- Reset any previous adjustments
	mp.command("no-osd vf remove @sync")
	mp.command("no-osd af remove @sync")

	if mp.get_property_bool("pause") == false then
		-- If already playing, start the sync fix
		mp.add_timeout(1, fix_sync)
	else
		-- If paused, wait for unpause. We need the video to be playing to measure drops
		local function wait_for_start(name, paused)
			if paused == false then
				-- The video is playing, start the sync fix
				mp.unobserve_property(wait_for_start)
				mp.add_timeout(1, fix_sync)
			end
		end
		mp.observe_property("pause", "bool", wait_for_start)
	end
end)

Full description:

MPV script that fixes video sync on some broken videos where both the audio and video PTS are incorrect by a constant factor. This is appearent on some videos exported from Topaz VEAI from the looks of it. This essentially works by measuring how much frames drop due to display sync and calculating the correct video fps and changes it via the setpts video filter, as well as audio via asetpts. Requires video-sync=display-*. To get a more accurate drop rate reading, a timeout is induced, meaning it'll take 2 seconds to actually take effect. On normal videos, they are left alone. It's activation rule is when the frames dropped per second is more than 50% of the container frame rate. In most cases, this is enough.

Also this does not work with both video-sync=display-* and the asetpts=N/SR/TB af filter. Just remove that asetpts, its useless with this script.