If you are seeing a black screen with sound when trying to playback a video, it could be due to several different causes:

1. Are you using an external monitor or airplay? If so, try using the built-in monitor instead.

2. Do you have any screen capture apps open, such as Chrome Remote Desktop? If so, quit them and try playing the video again.

3. Try quitting all other apps and playing the video again. If it now works, there might be an issue with a different app that the system thinks is trying to steal copyrighted content using screen recording.

4. Do you have an iPad connected using Sidecar? If so, try disconnecting and replaying the video.

5. Does your computer have dual-GPUs? If so, try downloading a separate piece of software called gfxCardStatus and force your computer to use the Intel-based GPU.

If none of the above apply to you, try the following: 

1) Boot into Recovery Mode on your Mac (hold down command+R while computer is booting up)
2) Open Terminal and type in the command EXACTLY as written:
nvram 8be4df61-93ca-11d2-aa0d-00e098032b8c:epid_provisioned=%01%00%00%00

and then press RETURN

3. It will go back to the prompt. Type reboot and RETURN. 

Please contact us if you are still having issues after trying the above.