. . . . Unable to show my MP4 video codec files after upgrading to 2024 version . . . .
MP4 is not a video codec, it is a container file format which supports several video codecs and audio codecs internally.
We need more information to help diagnose the issue(s) you are having:
The specification of your computer system including Windows version and program version, see this topic for what is required, and please quote processor and graphics card make/model in full, and also what monitor/screen resolution(s) you are working with if this is a laptop.
I would suggest you put this information in your profile signature so we do not have to keep asking for it.
Are you getting any error messages, if so then please quote them in full or provide screenshots.
Are the graphics card/integrated GPU drivers up to date?
In the program settings, Device options tab, what are the Import, Processing and Export options set to?
Download and install MediaInfo and analyse one of the clips causing the issue and post the results, see this tutorial on how to setup MediaInfo and analyse a video clip for all the data required.
"mp4" is a container format, the actual codecs used to create and/or play such files can, and do, vary enormously!
So, we need rather more information, please.
From which previous version of Movie Studio have you upgraded? If your older version is 17 or earlier you are now running a totally different software.
Did that version play these problem files successfully?
Can you follow this tutorial and copy and paste here the results of a MediaInfo analysis of one of the problem files? The tutorial page includes a link to download the app if you do not already have it.
With the answers to these questions we, fellow-users, may well be able to offer suggestions on how to resolve the problem.