Skype encrypts its Skype-to-Skype traffic according to their FAQ.
https://support.skype.com/en/faq/FA31/does-skype-use-encrypt...
https://support.skype.com/en/faq/FA31/does-skype-use-encrypt...
Make up a new, random https URL. Something no one knows and no one would accidently hit. Message it to someone on Skype. Wait 5 minutes to see a bot from Microsoft hit your URL.
And another thing that worries me is if video chats between two Skype users do/can fall on the wrong hands. Could the video files be pushed to some of those porn websites out there as adult videos XXX????
> For instant messages, we use TLS (transport-level security) to encrypt your messages between your Skype client and the chat service in our cloud [...]
As expected, it's just network-level encryption, not end-to-end encryption.