Streamlink is a command-line program that opens streams with a native video player like VLC. It was forked from Livestreamer.

Install the Streamlink Helper and follow the setup instructions for the native companion. After that, you should see a context item in the popup to open a stream with Streamlink.

You can change the default click action in the popup in the advanced extension settings to be Streamlink. It’s currently not possible to make Streamlink the default action for notifications.