What API in Android is used to make reliable audio calls in custom app? I see for example in WhatsApp, that it gets notification about incoming call (probably from Firebase?), and then acts like "real call" (you can see active call within Bluetooth headset interface, which you can accept, reject or hang up, and if someone calls you via classic voice call, it will be automatically hanged up as busy). I didn't found any documentation about this, and found only full-fledged SDKs.

CodePudding user response：

When investigating Android features, it may help to look at the Android Open Source Project site: https://source.android.com/

What you are asking for appears to be 'Third Party Calling App': https://source.android.com/devices/tech/connect/third-party-call-apps

That document even links to a page on the main Android Developer site should you wish to build a voice call app: https://developer.android.com/guide/topics/connectivity/telecom/selfManaged