Video noit playing and different video thumbnail

[Sumeet Misra]

Guys I am from India and i just updated my 720 to 8.1
My video player is totally lagging worse
it is not playing my previously shooted videos !!
and the thumbnails in my camera roll for videos are different
they show a different image and when i play the Video a different video is played !!
its really irritating guys !!!!
Please help me with this !!
please give me a sollution !!!!