If your video work on Debug mode, but on Release you see only black screen, please, check the link to your video. If you use 'http' protocol there, you will need to add next string to your AndroidManifest.xml file. [Details here](https://developer.android.com/guide/topics/manifest/application-element#usesCleartextTraffic)
Usually clear playback can be read with all Video player. Then you should ensure content can be played without any issue with another player ([VideoLan/VLC](https://www.videolan.org/vlc/) is a good reference implementation)
If content is protected with an access token or any other http header, ensure you can access to you data with a wget call or a rest client app. You need to provide all needed access token / authentication parameters.