Please try installing the Visual C++ 2010 SP1 Redistributable. You can find that here.
If that doesn't help, here are some steps to try fixing the video player issue:
- Exit VRChat.
- Press your Windows Key + R and type "certmgr.msc" into the window. Press ok. You can also type this into the Windows search bar.
- Go to Menu, then Action, then Find Certificates.
- In the "Contains" field, type "google".
- In the "Look in fields:" field, choose "issued to".
- Click "Find Now".
- Select all the expired certificates.
- Right click and choose "Delete".
Additionally, you may need to install the Windows Media Feature pack, which you can find here.If you have apostrophes in your file path (for example, "User's Files" as part of your folder name) that leads to the youtube-dl.exe program, the program can fail to run. You'll want to try removing those symbols to see if they're breaking video players.
As a final note, we've heard that the program Razer Cortex can cause this issue. Please try uninstalling it if applicable.