I want to import a .mp4 Video into Hitfilm Express, and it worked before, but now I get the Error above. I didnt changed anything or so.
@liveside Same .mp4 that worked before or a different one? Also which version of HFE? Also, please list your system specs.
A MediaInfo Tree report would go a long way to helping troubleshoot. How to use it here: https://www.google.com/search?client=firefox-b-1-d&q=mediainfo+how+to
System specs might be helpful, CPU, GPU, OS, RAM and Storage.
Checking your GPU drivers are current is a good idea, especially if you recently ran a Windows Update. Windows Update has been known to roll GPU drivers back to earlier versions. Otherwise, a MediaInfo report is also helpful.
Along with the above, I also found that clearing your HitFilm cache helps sometimes. Sometimes a cached file goes wonky.
Also, confirm that you have space left on your CACHE drive.
You can find where your cache is (and also clear the cache) by going into Hitfilm - File - Option - Cache.