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I'm currently implementing a sound effect mixing on Android via OpenSL. I have an initial implementation going, but I've encountered some issues.

My implementation is as follows:

1) For each sound effect I create several AudioPlayer objects (one for each simultaneous sound) that uses an SLDataLocator_AndroidFD data source that in turn refers to an OGG file. For example, if I have a gun firing sound (lets call it gun.ogg) that is played in rapid succession, I use around 5 AudioPlayer objects that refer to the same gun.ogg audio source and also the same outputmix object.

2) When I need to play that sound effect, I search through all the AudioPlayer objects I created and find one that isn't currently in the SL_PLAYSTATE_PLAYING state and use it to play the effect.

3) Before playing a clip, I seek to the start of it using SLPlayItf::SetPosition.

This is working out alright so far, but there is some crackling noise that occurs when playing sounds in rapid succession. I read on the Android NDK newsgroup that OpenSL on Android has problems with switching data sources. Has anyone come across this issue?

I'm also wondering if anyone else seen or come up with a sound mixing approach for OpenSL on Android. If so, does your approach differ from mine? Any advice on the crackling noise?

I've scoured the internet for OpenSL documentation and example code, but there isn't much out there with regards to mixing (only loading which I've figured out already). Any help would be greatly appreciated.

Mark
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This is probably not the best approach (creating many instances of audio players). Unfortunately the Android version (2.3) of OpenSL ES doesn't support SLDynamicSourceItf. Which would be similar to OpenAL's source binding interface. One approach would be to create multiple stream players. You would then search for a stream player that isn't currently playing and start streaming your sound effect to it from memory. It's not ideal but it's doable.

You should probably not use the ogg format for sound effects either. You're better off with WAV (PCM) as it won't need to be decoded.

Ogg is fine for streaming background music.

Byron
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