Android - high performance audio - how to do it

I've just been through a very interesting period of work, sorting-out a high-performance audio interface for the Android port of Mixtikl. I've learned quite a few things - here are the highlights.

Firstly, target Android 2.3 or later. This allows you to use OpenSL ES, which is the only realistic approach for low-latency audio on Android. The audio allows you to delivery audio with pretty low latency, and totally avoids any problems of garbage collection blocking you. This of course assumes that all your audio code is written in C++!

As you're using OpenSL ES, and assuming you have some very heavy audio DSP going-on (like in Mixtikl!), you'll need to use a separate Posix thread to keep your audio callbacks pumped-up. Basically, if your OpenSL ES audio block callbacks take much time at all, then your audio will break-up. So, use a worker thread to keep sufficient audio pre-processed and ready to be picked-up and delivered via your callbacks!

Finally, and believe me this is important (!): make sure you target armeabi-v7a, and that you use the right compiler flags to generate 32-bit ARM7 code. If you on the other hand use the default settings, you'll generate Thumb code for armeabi - and your code will run staggeringly slower  (!!), and audio break-up is inevitable if you're doing anything serious. So: don't bother targeting armeabi devices... and Thumb code is a no-no.

Follow my advice, and you can create sophisticated audio software. Don't follow it, and you're going to find things tough! ;)

I should note that support for  armeabi-v7a *emulator* targets arrived in the Android 4.0 SDK... which makes things a lot easier as well... something worth knowing!

Finally... here is a useful resource on the background to OpenSL ES on Android...:
http://mobilepearls.com/labs/native-android-api/opensles/index.html