If you are experiencing issues with video playback, please try the following troubleshooting steps to resolve the problem:

For Web:

Blank screen: Ensure that your web browser is up to date. Clear your browser's cache and cookies, then restart the browser. Try rejoining the classes after completing these steps.

Video stuck during playback: Check your internet speed to ensure it is stable. If the speed is satisfactory, try restarting the video. To improve performance, avoid using multiple tabs simultaneously and focus on one tab at a time.

Buffering: Verify your internet speed and consider restarting the video with a lower quality setting, such as 360p or 480p. This can help alleviate buffering issues and allow smooth playback.

For Mobile Application:

Blank screen or failure to start: Troubleshoot the Testbook app by updating it to the latest version. On your device, go to the main menu, tap and hold the Testbook app, then select "More Info." Next, access the "Data Storage" option and clear the app's cache. Afterward, reboot your phone or device, reopen the Testbook app, and attempt to play the videos again.

I hope these troubleshooting steps are helpful in resolving the video playback issues. If you continue to experience problems, please provide additional details about the specific error or issue you are encountering.

In this case first, reboot your device once and check but if the issue persists, check your internet connection and stability then retry accordingly.

Also if you are checking downloaded videos then please note you have kept your data connection on initially while watching downloaded video too and class will be working fine.