Walkie-talkie PoC

[®om]

Hi,

Thanks to your help, I wrote a proof-of-concept of push-to-talk feature for Batphone.
It is for real-time communication only (it is not the "voice mail" you have planned to implement).

I integrated it quickly-and-dirtily in the peer list (Contacts > "List phones on the mesh"):
http://dl.rom1v.com/batphone-walkie-talkie.png
Just select the recipients with the checkbox I added and push "TALK" button (yes, this button is awful).
On the screenshot, the first and third peers are selected.

The feature is available here:
https://github.com/rom1v/batphone/commits/walkietalkie

It depends on MDP sockets feature:
https://github.com/servalproject/batphone/pull/51
https://github.com/servalproject/serval-dna/pull/53

So you have to pull walkietalkie branch on batphone and mdpsock on serval-dna.

All batphones must be in PeerList activity for receving/sending audio packets (it is very easy to listen from any activity, as walkie-talkie is an Android service, but for the moment I only start it in PeerList.onResume() and stop it in PeerList.onPause()).

Walkie-talkie implementation is full-java.
Audio is captured at 8kHz and encoded in A-Law (8 bits).
It is packetized in a very simple protocol (10 bits for headers: 2 for packet sequence id, 4 for timestamp, 4 for source id).
Each packet is sent n times if there are n recipients.
The receiver is able to receive multiple audio streams and mix them together.
It uses a constant network cache of 100ms (AudioReceiver.DELAY_IN_MS).

There is no echo canceller, so you should test with headsets.

On client mode, I tested with 7 phones connected to a 8th configured as AP (each person having a headset). It worked very well.
On ad-hoc mode, I had some independant problems:
 - not all my phones work in ad-hoc mode ;
 - some working phones don't detect each other (see https://github.com/servalproject/serval-dna/issues/52#issuecomment-14559387).

I successfully tested with 3 phones in ad-hoc mode.

If you are interested in adding such a push-to-talk feature in Batphone, I think there is some work remaining: factorizing some parts with 1-to-1 communications for removing redundancy, maybe moving some code to native part (I read somewhere you wanted to do that for rhizome), using a better codec like opus or speex (for the moment it takes 64Kbps per recipient, which is huge), using a standard protocol like RTP, provide a better UI than my PeerList-hack...

Feedbacks are welcome.

[®om]

I just built an APK to make it easier to test: batphone-walkietalkie-debug.apk.

I included bugfix of #71 for avoiding random crashes in the peer list.

This apk was generated with these versions:
batphone: merge of 159eaf8 (walkietalkie) and aa36438 (bug71).
serval-dna: 69e7f7a (mdpsock).