well i can give the tip ,try to search the
www.s1fw.com,but dont ever try to fix your player with the same ID like yours(QY781FV2) ,try the other firmware's too.Secondly the screen plate ID is very important is it TFT series or the CM series and search with the screen ID too.Finally and the most important if you are searching the firmware for the AK1025 then dont ever stuck your self on the AK1025 firmwares ,definlaty try the ATJ2091 firmwares on the AK1025 chip ............. i hope if you work hard then you get your mp4 fixed.
GOOD LUCK
)