我在 android 上采样音频，并基于此将一些 RGB 值发送到使用蓝牙的 arduino 设备。
发送的音频样本和 arduino 做出反应之间有很长的延迟（几秒钟）。我假设这是由于 android 比 arduino 快得多，并且在传输字节被备份到手机缓冲区的地方进行了某种流控制。连接蓝牙的代码是：
mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
mmSocket.connect();
mmOutputStream = mmSocket.getOutputStream();
然后发送数据：
mmOutputStream.write(0xFF);
mmOutputStream.write(outputFreq);
mmOutputStream.write(outputMagnitude);
我不介意丢失数据，因为我只需要发送最新的值。
实现这一目标的最佳方法是什么？我是 Android 编程的新手，希望它能够很快工作，所以更简单的解决方案会更好！我已经考虑过某种堆栈，以及一个在计时器上运行的单独线程，它会浏览堆栈顶部并仅发送这些值，但这听起来很复杂，因为我对线程编程一无所知。
有没有办法配置outputstream它只是丢弃没有及时发送的数据？
如果有任何帮助，这是完整的代码：
package com.example.fft1;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.UUID;
import com.androidplot.series.XYSeries;
import com.androidplot.xy.BoundaryMode;
import com.androidplot.xy.LineAndPointFormatter;
import com.androidplot.xy.XYPlot;
import com.androidplot.xy.SimpleXYSeries;
import edu.emory.mathcs.jtransforms.fft.DoubleFFT_1D;
import android.graphics.Color;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
XYPlot plot;
SimpleXYSeries plotSeries;
AudioRecord audioRecord;
RecordAudio recordTask;
int frequency = 44100;
int channelConfiguration = AudioFormat.CHANNEL_IN_MONO;
int audioEncoding = AudioFormat.ENCODING_PCM_16BIT;
BluetoothAdapter mBluetoothAdapter;
BluetoothSocket mmSocket;
BluetoothDevice mmDevice;
OutputStream mmOutputStream;
InputStream mmInputStream;
int counter;
@SuppressWarnings("deprecation")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialize our XYPlot reference:
plot = (XYPlot) findViewById(R.id.mySimpleXYPlot);
plot.setRangeBoundaries(-1000000, 1000000, BoundaryMode.FIXED);
Number[] seriesData = {1,2,3,4,5,6};
// Turn the above arrays into XYSeries':
plotSeries = new SimpleXYSeries(
Arrays.asList(seriesData), // SimpleXYSeries takes a List so turn our array into a List
SimpleXYSeries.ArrayFormat.Y_VALS_ONLY, // Y_VALS_ONLY means use the element index as the x value
"Series1"); // Set the display title of the series
// Create a formatter to use for drawing a series using LineAndPointRenderer:
@SuppressWarnings("deprecation")
LineAndPointFormatter series1Format = new LineAndPointFormatter(
Color.rgb(0, 200, 0), // line color
Color.rgb(0, 100, 0), // point color
null); // fill color (none)
// add a new series' to the xyplot:
plot.addSeries(plotSeries, series1Format);
// reduce the number of range labels
plot.setTicksPerRangeLabel(3);
// by default, AndroidPlot displays developer guides to aid in laying out your plot.
// To get rid of them call disableAllMarkup():
plot.disableAllMarkup();
Button startBtn = (Button)findViewById(R.id.startButton);
int bufferSize = AudioRecord.getMinBufferSize(frequency, channelConfiguration, audioEncoding);
audioRecord = new AudioRecord(
MediaRecorder.AudioSource.DEFAULT,
frequency,
channelConfiguration,
audioEncoding,
bufferSize
);
startBtn.setOnClickListener(new startBtnClick());
Button connectBtn = (Button)findViewById(R.id.connectBtn);
connectBtn.setOnClickListener(new connectBtnClick());
}
class startBtnClick implements Button.OnClickListener {
@Override
public void onClick(View view) {
Button button = (Button) view;
if (button.getText().toString().equals("Start")) {
button.setText("Stop");
recordTask = new RecordAudio();
recordTask.execute();
} else {
button.setText("Start");
recordTask.cancel(false);
}
}
}
class connectBtnClick implements Button.OnClickListener {
@Override
public void onClick(View view) {
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if(!mBluetoothAdapter.isEnabled()) {
Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBluetooth, 0);
}
Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
if(pairedDevices.size() > 0) {
for(BluetoothDevice device : pairedDevices) {
Log.v("BT2", "Device: " + device.getName());
if(device.getName().equals("linvor")) {
mmDevice = device;
break;
}
}
}
UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb"); //Standard SerialPortService ID
try {
mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
mmSocket.connect();
mmOutputStream = mmSocket.getOutputStream();
mmInputStream = mmSocket.getInputStream();
for (int i = 0; i < 255; i++) {
mmOutputStream.write(0xFF);
mmOutputStream.write(i);
mmOutputStream.write(255);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//beginListenForData();
}
private class RecordAudio extends AsyncTask<Void, Integer[], Void> {
@Override
protected Void doInBackground(Void... params) {
int blockSize = 128;
short[] buffer = new short[blockSize];
double[] bufferD = new double[blockSize];
audioRecord.startRecording();
// Here's the Fast Fourier Transform from JTransforms
DoubleFFT_1D fft = new DoubleFFT_1D(buffer.length);
while (!isCancelled()) {
counter = (counter + 1) % 1000;
//Log.v("FFT1", String.valueOf(counter));
int sumEnergy = 0;
logTime("start");
// Read audio to 'samples' array and convert it to double[]
audioRecord.read(buffer, 0, buffer.length);
logTime("after reading");
for (int i = 0; i < buffer.length; i++) {
bufferD[i]=buffer[i];
}
fft.realForward(bufferD);
logTime("after fft");
Integer[] spectrum = new Integer[blockSize/2];
for (int k = 0; k < blockSize / 2; k++) {
spectrum[k] = new Integer((int) Math.sqrt( (bufferD[2*k] * bufferD[2*k]) + (bufferD[2*k+1] * bufferD[2*k+1]) ));
}
int averageMagnitude = 0;
int middleFreqBin = 0;
for (int i = 0; i < spectrum.length; i++) {
averageMagnitude += spectrum[i];
}
averageMagnitude /= spectrum.length;
int halfMagnitudeSum = 0;
for (int i = 0; i < spectrum.length / 2; i++) {
halfMagnitudeSum += spectrum[i] * i;
}
halfMagnitudeSum /= 2;
int runningTotal = 0;
for (int i = 0; i < spectrum.length; i++) {
runningTotal += spectrum[i] * i;
if (runningTotal > halfMagnitudeSum) {
middleFreqBin = i;
break;
}
}
int outputMagnitude = map(averageMagnitude, 0, 50000, 0, 254);
int outputFreq = map(middleFreqBin, 0, spectrum.length, 0, 254);
if (outputMagnitude > 254) outputMagnitude = 254;
try {
//Log.v("FFT1", "OutputFreq: " + outputFreq + ", outputMagnitude: " + outputMagnitude);
mmOutputStream.write(0xFF);
mmOutputStream.write(outputFreq);
mmOutputStream.write(outputMagnitude);
Thread.sleep(10);
} catch (Exception e) {
// TODO Auto-generated catch block
Log.v("FFT1","Not connected");
}
logTime("after bluetooth");
publishProgress(spectrum);
}
return null;
}
protected void onCancelled() {
audioRecord.stop();
}
protected void onProgressUpdate(Integer[]... args) {
Integer[] spectrum = args[0];
plotSeries.setModel(Arrays.asList(spectrum), SimpleXYSeries.ArrayFormat.Y_VALS_ONLY);
plot.redraw();
}
int map(int x, int in_min, int in_max, int out_min, int out_max) {
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public void logTime(String text) {
if (counter < 5) {
String time = String.valueOf(new java.util.Date().getTime());
Log.v("FFT1", text + ": " + time.substring(time.length()-4, time.length()));
}
}
}