in the beginning my video player worked great, but now the sound and the video are almost in slomo
deleted all my file and downloaded the games and video player from the internet again.
downloaded the videos again and it still sucks

somebody has knowelege and can help?

I can only guess, but I'd first look into defragmenting the SD card's file system.

On windows you can start the command line as administrator and execute

Code Select Expand

defrag k: /d
... when k is the drive letter.