Bandicam usually uses 'Screen Recording' mode to record Skype video calls.
To record the Skype calls, please visit https://www.bandicam.com/how-to/screen-recorder/
With Bandicam, you can record Skype calls, your voice, your friend's voice, game/computer sounds at the same time.
If you can't record the Skype calls (Your voice and Your friend's voice), please check the settings below:
When you start Skype, Skype/Windows will change your computer volume automatically.
When you are talking with your friends in Skype, "Stereo Mix" may be unchecked by Windows.
To record game/program/video/audio sounds with Skype, you should re-check "Stereo Mix" while you are talking and increase the "Stereo Mix" volume.
When you are talking with your friends in Skype, the "game/program/video/audio sounds" will be reduced by Windows.
To record game/program/video/audio sounds with Skype, check "Do nothing" under the "Communications" tab in Windows.
And then, check the volume mixer while you are talking.