If you are using an Android device and discover that a video has no sound, please check the following:
Check the Side Switch
The app utilizes the Android native video player and in many cases, the sound does not play because the device has been muted. Check the side of the device and confirm that your volume is turned up.
Check the Control Center
Launch the Control Center by swiping up from the bottom of your screen. Look for a bell with a line through it. It will be one of six icons in the middle of the Control Center. If the bell is white, tap on it to turn it black (the off position), then try launching an app with sound to see if your audio has returned
Turn the Sound All the Way Up
In some cases, turning he sound all the way up will correct the issue.