Android - How to open the Hangout app from a Hangout URL displayed in the webview?
You can use WebViewClient.shouldOverrideUrlLoading to catch these links and then start an appropriate activity. A good example of how to launch the Google Play app this way is described here: Allow all 'market://' links from inside a webview to open Google Play store
Start video calls with Google hangouts on Android
It appears that there is currently no way to do this using an Intent.
Currently, the Google+ Hangouts Button only works for web apps.
Feature request here: http://code.google.com/p/google-plus-platform/issues/detail?id=385
Google Hangouts API: Can I start an On Air Hangout?
It is not currently possible to embed a hangout. With the Hangout button, though, the start screen includes the standard checkbox to make the Hangout On Air. developers.google.com/+/hangouts/button
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