窃听（聚焦）音频流android

Question

Despite reading everything I can on developer.android.com and stackoverflow I cannot figure out how to do this, though I really think it should be possible.

I'm trying to make a generic "visualizer"-style app using OpenGL ES 2.0. I would like to be able to eavesdrop on whatever audio stream currently has focus so that I can respond to the music. The device should be able to play music from any app they want, but then open my app and have it respond.

So far I've found plenty of ways to play, record, stream, etc. audio from a known source. However, I cannot figure out how to eavesdrop on the device. On the mac this is as simple as inserting an audio unit at the hardware side. Is there anything similar in android? Or does sandboxing prevent this entirely?

Answer 1

Here's another way of looking that this issue. Suppose the OS let you do this. Suppose there was an API that let you do

Audio.doEavesDrop(EavesDrop callback)

Now, imagine what some of the negative consequences could be:

• hanging the audio stream. That callback has return control at sometime, what if it doesn't for some reason? What happens to the audio stream?

• maliciously eaves dropping: your employer or a blackmailer, or someone else who wants to invade your privacy uses this to capture every sound your phone outputs

If you were designing the platform how would you defend against this issues (and these are only the ones I could think of in a few minutes).

Do you think this should be possible? Maybe it isn't and there is(are) good reason(s) for it.