恢复时的Android AudioTrack延迟

Question

I have an application that needs to pause and resume an AudioTrack quite frequently and this issue has been tested and seen on multiple devices. When the AudioTrack is played and paused, don't do anything in a few seconds, then resume the audio, then there's a delay, about 0.3 secs. If you then pause and resume it immediately, there will be no delay.

Here's the logcat when there is no delay: (from cm-11-20140521-NIGHTLY-i9500)

D/AudioFlinger( 2578): start(4098), calling pid 13180 session 3204
D/AudioFlinger( 2578): PAUSED => RESUMING (4098) on thread 0xb730ae40

Here's the logcat when there is delay:

D/AudioFlinger( 2578): start(4098), calling pid 13180 session 3204
D/AudioFlinger( 2578): PAUSED => RESUMING (4098) on thread 0xb730ae40
V/audio_hw_primary( 2578): start_output_stream: starting stream
V/audio_hw_primary( 2578): start_output_stream: stream out device: 2, actual: 2

And I guess it's the start_output_stream thing or GC that causes the delay. Does anyone know how to fix this?

PS Here's the background code:

public boolean onTouch(View view, MotionEvent motionevent) {
    switch (motionevent.getAction()) {
        case MotionEvent.ACTION_DOWN:
            pressed = true;
            (new Thread(new Runnable() {
                public void run() {
                    /* Generate savedTrack */
                    if (pressed) savedTrack.play();
                }
            })).start();
            return true;
        case MotionEvent.ACTION_UP:
            pressed = false;
            if (savedTrack != null) savedTrack.pause();
            return true;
    }
    return false;
}

Answer 1

Okay it turns out that if there is no STREAM_MUSIC audio playing for a while, the output device/stream will shut itself down and causes a delay when resuming the audio. So the solution is simple: play a muted looped track in the background when the app is foreground.

Another thing I noticed is that if your AudioTrack is less than 16 samples, it won't loop. Hope this help.