Using the
js_ReaScriptAPI extension you could try something like this,
Code:
local title = reaper.JS_Localize('Resources', 'common')
local hwnd = reaper.JS_Window_FindTop(title, true)
local filter = reaper.JS_Window_FindChildByID(hwnd, 0x466)
if filter then
local track = reaper.GetSelectedTrack(0, 0) -- get first selected track
if not track then
reaper.JS_Window_SetTitle(filter, "") -- erase text in filter
else -- set filter to name of first selected track
local _, track_name = reaper.GetSetMediaTrackInfo_String(track, "P_NAME", "", false)
reaper.JS_Window_SetTitle(filter, track_name)
end
end