Please help with mkv/mp4 video file corruption..

[BPetk7]

So, I AM new to Android Central so if I'm posting incorrectly/wrong forum or JAI, please let me know.
This has happened on my current Samsung A12 AS WELL AS my previous android 9.
When I now copy MKV/MP4 videos(regardless via usb cable or inserted into pc) to my sd card, they will not play on Phone.
Does not matter what video player, VLC or ANY other. No Codec needed. KIM, it DOES sometimes work and I have NO problem. I DO NOT get any errors. It just won't play.
They DO PLAY fine before transferring. They also play fine AFTER copying to sd card BUT prior to inserting it into phone.
It's as if the phone corrupts it immediately after inserting card into phone.
I do not have another sd card to see if it's a bad card but I currently have other video files that I had transferred awhile back and they play fine on phone.
NOTE: Yes, I have already formatted and REFORMATTED the card to make sure, as well as verified integrity of sd card with check.

 

[B. Diddy]

Welcome to Android Central! I moved this from the Android 11 forum to the General Help forum, since I doubt it's a problem specific to Android 11.

Do the videos work if you copy them to Internal Storage instead of the SD?

SD cards are so cheap these days that I would still recommend trying a different card. A card can get corrupt and cause somewhat specific issues, but otherwise seem to work ok.