我正在使用Java声音API和Java 1.7。当我在Linux上运行我的应用程序时，我很难快速地从TargetDataLine读取以跟上记录的内容（java版“1.7.0_51”，Java（TM）SE运行时环境（版本1.7.0_51-b13）， Java HotSpot（TM）64位服务器VM（构建24.51-b03，混合模式），Red Hat Enterprise Linux 5）。在我的Windows 7笔记本电脑上运行相同的程序时，我没有这个问题。我有点难过。
为了隔离这个问题，我编写了一个程序，它从TargetDataLine中捕获一段时间（交互式确定），并记录每次阻塞读取固定字节数所花费的时间，然后打印出来以及平均阅读时间，已用时间和录制音频的时间。
我的测试程序如下：
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.DataLine;
import javax.sound.sampled.LineUnavailableException;
import javax.sound.sampled.Mixer;
import javax.sound.sampled.TargetDataLine;
/**
* This is a test of mic capture delay for given buffer and fetch settings.
*/
public class MicCaptureDelayTest {
/**
* the audio format used for capturing and transmitting
*/
private static final AudioFormat format =
new AudioFormat(8000, 16, 1, true, true);
/**
* This is the target data line buffer size to request, in bytes.
*/
private static final int MIC_BUFFER_SIZE = 1000;
/**
* This is the number of bytes to try to fetch from the target data line at a
* time.
*/
private static final int MIC_FETCH_SIZE = 480;
/**
* Searches for available mixers on the system that have a microphone.
* @return a list of matching mixers
*/
private static List<Mixer.Info> findMicrophoneMixers() {
Mixer.Info[] mixerInfos = AudioSystem.getMixerInfo();
List<Mixer.Info> matches = new ArrayList<>();
for (Mixer.Info mixerInfo : mixerInfos) {
Mixer mixer = AudioSystem.getMixer(mixerInfo);
DataLine.Info lineInfo = new DataLine.Info(TargetDataLine.class,
format);
boolean isSupported = mixer.isLineSupported(lineInfo);
if (isSupported) {
matches.add(mixerInfo);
}
}
return matches;
}
/**
* This is the test recording thread.
*/
private static class MicFetcher extends Thread {
/**
* This is the requested recording state.
*/
private boolean shouldRecord = false;
/**
* This is the current processed recording state of the thread.
*/
private boolean isRecording = false;
/**
* This is the Java audio interface line microphone data is captured from.
*/
private TargetDataLine lineFromMic;
/**
* Runs the test mic capture thread body.
*/
@Override
public void run() {
List<Mixer.Info> matchingMixerInfo = findMicrophoneMixers();
// Use the first matching mixer.
Mixer mixerToUse = AudioSystem.getMixer(matchingMixerInfo.get(0));
DataLine.Info info = new DataLine.Info(TargetDataLine.class, format);
try {
lineFromMic = (TargetDataLine) mixerToUse.getLine(info);
lineFromMic.open(format, MIC_BUFFER_SIZE);
} catch (LineUnavailableException e) {
e.printStackTrace();
return;
}
byte[] transferBuffer = new byte[MIC_FETCH_SIZE];
List<Long> readTimesNanos = new LinkedList<>();
int numFramesCaptured = 0;
long startTimeNanos = 0;
while (true) {
boolean currentShouldRecord;
synchronized(this) {
currentShouldRecord = shouldRecord;
}
if (!isRecording && currentShouldRecord) {
// Start recording.
System.out.println("Starting.");
lineFromMic.start();
isRecording = true;
startTimeNanos = System.nanoTime();
} else if (isRecording && !currentShouldRecord) {
// Stop recording.
System.out.println("Stopping.");
lineFromMic.stop();
lineFromMic.flush();
System.out.print("read times (ms): ");
long sumReadTimesNanos = 0;
int i = 0;
for (Long sampleTimeNanos : readTimesNanos) {
if (i % 5 == 0) {
System.out.println();
}
System.out.printf("%.2f ", sampleTimeNanos / 1.0e6);
sumReadTimesNanos += sampleTimeNanos;
++i;
}
System.out.println();
System.out.println(
"Mean read time (ms): "
+ (sumReadTimesNanos / 1.0e6
/ readTimesNanos.size()));
long stopTimeNanos = System.nanoTime();
System.out.println("Time captured (s): "
+ (numFramesCaptured / format.getFrameRate()));
System.out.println("Time elapsed (s): "
+ (stopTimeNanos - startTimeNanos) / 1.0e9);
readTimesNanos.clear();
numFramesCaptured = 0;
isRecording = false;
} else if (isRecording) {
// Continue recording.
long beforeTimeNanos = System.nanoTime();
// Retrieve data from the line. This blocks.
int numBytesRead = lineFromMic.read(
transferBuffer, 0, MIC_FETCH_SIZE);
numFramesCaptured += numBytesRead / format.getFrameSize();
long afterTimeNanos = System.nanoTime();
long timeElapsedNanos = afterTimeNanos - beforeTimeNanos;
readTimesNanos.add(timeElapsedNanos);
}
}
}
/**
* Requests to toggle the recording state of the test recording thread.
*/
public synchronized void toggleState() {
shouldRecord = ! shouldRecord;
}
}
/**
* Runs the test program. Newline toggles state.
* @param args command line args-- none needed
* @throws IOException if thrown when trying to get console input
*/
public static void main(String[] args) throws IOException {
BufferedReader inputReader =
new BufferedReader(new InputStreamReader(System.in));
MicFetcher fetcher = new MicFetcher();
fetcher.start();
while (true) {
// Toggle state for each line of input (ie, press enter to toggle).
inputReader.readLine();
fetcher.toggleState();
}
}
}
当我在Linux环境中运行时，大约10秒钟的录音，输出如下：
Starting.
Stopping.
read times (ms):
54.00 18.10 36.62 36.32 35.99
18.10 18.25 54.26 18.30 35.56
18.12 35.51 36.74 17.22 36.70
35.29 18.33 35.60 18.23 54.72
19.00 37.99 18.14 18.37 53.91
18.37 35.34 36.00 18.00 36.00
18.00 54.71 17.22 18.12 36.18
36.64 36.08 18.00 54.34 18.26
18.27 35.44 18.30 54.77 18.33
18.24 36.51 35.47 36.52 18.35
17.14 54.96 18.13 36.73 17.21
54.95 18.28 18.37 36.54 36.72
35.56 18.37 17.23 54.46 18.36
35.53 18.08 36.00 36.00 17.99
54.30 18.06 35.22 18.00 18.00
53.93 18.32 35.63 36.64 18.16
35.21 18.30 55.65 18.23 18.35
35.55 36.32 35.60 18.30 36.33
36.21 17.22 36.54 18.32 54.96
17.19 18.36 35.62 36.67 35.25
18.29 18.37 54.63 18.37 36.54
18.35 53.91 18.37 17.23 36.70
36.09 36.01 17.19 18.33 53.91
18.37 36.56 18.36 35.53 36.58
18.16 53.84 18.26 36.03 18.08
18.12 54.24 18.08 36.14 36.19
18.12 36.08 18.11 53.80 18.28
18.37 36.55 18.13 53.99 18.00
36.12 35.54 18.28 36.56 17.20
53.96 18.00 18.01 36.67 36.53
36.71 17.19 18.37 54.37 18.02
35.97 18.00 54.00 18.00 18.00
36.00 35.99 36.34 18.37 18.35
53.93 18.13 36.63 18.33 36.33
36.34 18.33 36.55 35.51 36.66
18.29 18.06 54.00 17.99 36.08
18.25 36.64 36.38 18.37 35.55
36.66 18.21 36.73 17.19 54.27
18.13 35.55 18.18 36.31 35.56
18.34 53.90 18.36 18.09 36.15
18.22 53.90 18.32 18.37 53.89
18.19 36.04 17.20 53.94 18.31
18.37 36.55 36.70 36.61 18.35
17.18 53.97 18.32 36.55 19.01
18.99 57.00 18.99 38.01 18.98
38.00 18.99 36.99 36.35 18.37
36.55 36.70 18.04 38.00 19.00
38.00 37.99 18.99 37.99 19.00
37.06 36.43 36.03 18.00 18.00
54.47 18.25 36.70 18.22 18.37
53.55 18.33 35.59 36.59 18.29
35.36 18.37 54.89 18.24 36.44
18.33 18.36 53.52 18.13 36.36
35.57 18.20 35.52 18.20 53.78
18.18 18.16 35.49 36.67 36.54
18.37 36.53 36.67 17.19 36.65
18.29 54.87 17.14 18.24 36.68
35.49 35.61 18.27 18.36 53.77
18.24 35.43 18.35 53.90 18.37
18.24 38.00 38.00 37.99 18.99
19.01 37.98 19.00 57.00 18.99
19.00 38.00 18.99 55.01 18.98
35.99 18.00 18.01 54.98 18.00
37.00 17.99 36.00 36.00 17.99
54.01 18.98 18.00 36.02 18.98
53.16 18.34 35.59 36.20 17.98
36.00 18.00 54.00 17.99 18.00
36.00 35.99 36.01 17.99 18.00
54.00 17.98 35.99 18.00 54.28
Mean read time (ms): 30.210176811594206
Time captured (s): 10.35
Time elapsed (s): 10.466399
在我的Windows环境中类似的大约10秒录制的输出如下所示：
Starting.
Stopping.
read times (ms):
44.96 30.13 29.97 29.97 30.04
29.96 29.96 30.00 29.99 30.00
29.92 30.01 30.02 30.01 29.99
29.85 45.12 30.03 29.92 29.96
29.98 30.00 29.98 30.00 0.24
44.73 29.94 30.04 29.96 29.86
29.96 30.05 29.85 30.17 30.02
30.00 29.94 29.99 29.99 30.04
29.97 44.99 29.99 30.08 29.88
30.05 29.95 29.97 29.87 0.15
44.95 29.98 29.91 30.08 29.98
30.00 30.01 29.96 29.94 30.04
30.01 29.96 29.88 30.00 29.95
30.04 44.99 29.99 29.96 30.03
30.00 30.07 29.94 30.01 0.21
44.77 29.95 30.02 30.01 30.00
29.96 29.98 30.00 30.00 29.94
29.99 30.04 29.93 29.99 30.02
29.98 44.99 29.99 29.96 30.01
30.03 29.95 30.00 29.97 0.21
44.81 29.88 30.05 29.99 29.99
30.01 29.97 29.99 29.99 29.98
29.99 30.00 29.97 29.98 29.97
30.01 44.95 29.97 30.03 30.00
30.00 30.00 29.99 29.97 0.21
44.79 29.95 30.00 29.99 29.95
29.98 29.93 30.06 29.94 30.08
29.97 30.00 29.97 29.99 29.98
29.94 45.05 30.04 29.91 30.00
29.99 29.97 30.01 29.98 0.21
44.79 29.94 29.99 29.89 30.06
30.03 29.96 30.04 29.98 29.90
30.04 30.00 29.98 30.00 29.97
30.07 44.96 29.98 29.93 30.07
29.98 29.90 30.00 29.94 0.13
44.97 29.98 29.99 29.94 30.02
30.00 29.93 29.99 30.02 30.01
29.99 29.96 30.02 29.90 29.93
30.01 45.04 30.06 29.99 29.98
29.94 30.04 30.00 29.92 0.20
44.83 29.94 29.99 30.00 30.01
30.02 29.87 30.03 29.94 30.03
29.99 30.00 30.07 29.90 29.95
30.05 44.97 30.01 29.98 29.97
30.01 29.99 30.00 29.97 0.21
44.77 29.96 30.00 30.03 29.91
30.00 30.01 30.03 29.93 29.98
29.99 29.99 29.93 30.04 30.04
30.01 44.92 30.04 29.97 29.91
30.08 29.89 29.97 29.88 0.15
45.01 30.09 29.89 30.01 30.01
29.97 29.95 29.96 30.05 30.04
29.88 30.00 29.99 29.94 30.05
29.98 44.99 30.01 30.00 29.99
29.95 30.00 29.88 30.11 0.21
44.78 30.01 29.96 29.99 29.98
29.98 29.99 30.01 29.91 29.82
30.10 29.99 30.15 29.96 29.93
29.98 45.05 29.97 29.99 30.02
29.96 29.98 29.95 30.04 0.21
44.74 30.02 29.97 29.97 30.03
29.99 29.93 29.94 30.07 29.99
29.99 29.94 30.02 29.97 29.90
30.01 45.12 29.91 30.03 29.95
30.03 29.97 29.87 30.09 0.20
44.79 29.98 29.97 29.99 30.01
30.01 29.97 29.99 29.99 30.01
29.99 29.94 30.01 30.00 29.98
29.98 45.02 29.97 29.91 30.06
29.99 29.96 30.02 29.98
Mean read time (ms): 30.073811959885386
Time captured (s): 10.47
Time elapsed (s): 10.777957116
关于Linux环境的摘要统计数据，大约30秒的记录：
Mean read time (ms): 30.152922254616133
Time captured (s): 30.87
Time elapsed (s): 31.135111
Windows环境的摘要统计信息，大约30秒录制：
Mean read time (ms): 30.020078674852652
Time captured (s): 30.54
Time elapsed (s): 30.901762071
我注意到，经过的时间和捕获的时间之间的差异随着Linux端记录时间的增加而增加。在Linux方面，单个获取时间看起来也不那么规律。
我已经尝试调整缓冲区和获取大小，但我还没有找到一个允许从线路中快速获取的组合。
什么可能导致取得缓慢？如何确定合理的提取和缓冲区大小，以便具有低延迟但快速提取以及时跟上实时？ Linux上是否存在可能影响此问题或我应该检查的声音配置问题？
谢谢！
答案 0 :(得分：1)
private static final int MIC_FETCH_SIZE = 480; // 0.12 seconds of data
这是一个非常小的缓冲区大小，以获得可靠的性能。在16位单声道时，它仅代表240个声音样本。使其更像16000个样本，或者：
private static final int MIC_FETCH_SIZE = 32000; // 2 seconds of data
注意： Java Sound不保证读取金额，而是返回 实际读取的字节数。关键是，允许机会读取最多 2秒的数据（如果可用）。
我认为这应解决上述大部分问题。