I have searched the net and found many users with this problem but no definitive solutions.

I have installed VLC and MX player but still cannot open files.

Ideas welcome.

The imported files were from messenger app

The files are playable on other devices

Serious issue.

2 hours ago, norbra said:

The imported files were from messenger app

What messenger is that?

In the past I noticed that some downloaded videos (Instagram downloads) sent through Signal messenger have strange effects like slow motion playback.

 

Just now I tried to send a music video in MP4 format with Signal (using attachment function) and it obviously does not even upload anything. Black box with the play button and nothing happens.

If I send it using the file send function the outcome plays OK.

I have a Samsung but not an S24.

50 minutes ago, KhunBENQ said:

What messenger is that?

In the past I noticed that some downloaded videos (Instagram downloads) sent through Signal messenger have strange effects like slow motion playback.

 

Just now I tried to send a music video in MP4 format with Signal (using attachment function) and it obviously does not even upload anything. Black box with the play button and nothing happens.

If I send it using the file send function the outcome plays OK.

I have a Samsung but not an S24.

Meta (Facebook) Messenger, mp4 files sent by Line app.

I have since converted these files to .avi format and sent them again via Line and they play fine.

Sounds like Codec issues.