Why does AudioRecord.getMinBufferSize return ERROR

问题:

I am testing this on a Samsung Galaxy S i9000.

int sampleRate = 44100;
int bufferSize = AudioRecord.getMinBufferSize(sampleRate, 
    AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_8BIT);

It returns -2 ERROR_BAD_VALUE.

The native sample rate is 44100Hz, as returned by

AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_SYSTEM).

I have tried setting sampleRate to 1000, 8000, 22100 and 44100. I have also tried changing AudioFormat.CHANNEL_IN_MONO to AudioFormat.CHANNEL_CONFIGURATION_MONO. I have also tried STEREO (both IN_STEREO and CONFIGURATION_STEREO). I have also tried 16 bit encoding instead of 8 bit.

Update: my Manifest has AUDIO_RECORD as permission.

I keep getting -2 as a result. Why is this happening?

回答1:

From the platform source file AudioRecord.java:

static public int getMinBufferSize(int sampleRateInHz, int channelConfig, int audioFormat) {
    ...
    // PCM_8BIT is not supported at the moment
    if (audioFormat != AudioFormat.ENCODING_PCM_16BIT) {
        loge("getMinBufferSize(): Invalid audio format.");
        return AudioRecord.ERROR_BAD_VALUE;
    }
    ...
}

Looks like your choice is 16-bit or nothing. :\

回答2:

In emulator it will always return -2. With the same code it will ok on real mobile.