在屏幕锁定/唤醒过程中遇到Android音频卡顿

Question

I'm working on an Android app centered around audio playback and I'm experiencing some erratic behavior (audio stuttering and hiccups) that I suspect might be inherent to certain devices, OS versions or perhaps the native buffer size of the device.

About my implementation - I'm in need of low latency so I'm processing my audio in OpenSL ES callbacks and using a fairly small buffer size of 128 samples to enqueue the buffers. I am doing mp3 decoding during the callback, but with my ring buffer size, I do not need to decode during every callback cycle.

I'm using a remote testing service to gauge audio playback quality on a variety of devices and OS versions and here's a few examples of the inconsistencies I'm finding.

• Samsung Galaxy S4 w/ Android 4.4 - no audio playback issues
• Samsung Galaxy S4 w/ Android 4.3 - user experiences audio drop-outs/stuttering when locking/un-locking the device
• Samsung Galaxy Note 2 w/ Android 4.1.2 - no issues
• Samsung Galaxy Note 2 w/ Android 4.3 - audio drop-outs during playback and stuttering when locking/unlocking screen.

Personally, I have a Galaxy S3 w/ 4.1.2 and a Nexus 5 with 4.4 and don't ever experience these issues. I also have a few older 2.3.7 devices where these issues do not occur (2010 Droid Incredible, LG Optimus Elite).

I am fairly confident that I'm not over-working the processor since I can get this running on older, Gingerbread devices just fine.

My questions:

1. If I raise my base SDK to 4.2, I can detect native buffer size from the hardware and use some multiple of this during my buffer queue callbacks. Would this make much of a difference in cases where stuttering and drop-outs are problematic especially during screen lock?
2. Is there a known bug with Android 4.3 where audio playback suffers, especially during screen lock actions? Is this possibly just a Samsung issue?
3. Are there other ways of improving performance to avoid this problem? I absolutely need OpenSL ES for my app.

Thanks.

Answer 1

Increasing buffer size solves some problems regarding distortion and noise. Yes, you can detect native buffer size from the hardware when your SDK is above 4.2 with this:

String size = audioManager.getProperty(AudioManager.PROPERTY_OUTPUT_FRAMES_PER_BUFFER);

But yet another approach to get the minimum buffer size for Audio Record is:

int minForAudioRecord = AudioRecord.getMinBufferSize(8000,
                AudioFormat.CHANNEL_IN_MONO,
                AudioFormat.ENCODING_PCM_16BIT);

And for Audio Playback:

int minForAudioTrack = AudioTrack.getMinBufferSize(8000,
                AudioFormat.CHANNEL_OUT_MONO,
                AudioFormat.ENCODING_PCM_16BIT);

If your SDK version is greater than or equal to 4.2, then you can have preferred sample rate for your audio.

String rate = audioManager.getProperty(AudioManager.PROPERTY_OUTPUT_SAMPLE_RATE);

I've found samsung devices are the worst while dealing with these things because each device has different approach to deal with audio drivers.