Java - 在 X 位置开始音频播放

Question

编辑： 我正在使用.wav文件

我正在尝试弄清楚如何在某个位置开始音频(例如：音频文件10秒而不是开始时(。阅读SourceDataLine的文档让我相信这可以在以下期间使用偏移量来实现：

line.write(byte[] b, int offset, int length)

但是每次我尝试 0(我相信是默认值(以外的任何值时，我都会得到java.lang.IndexOutOfBoundsException，也许它还没有读取 x 字节位置，所以不能写入 x 字节位置？我不确定，挠了挠头。

我认为这将是一个足够常见的请求，但似乎无法在网上找到与此相关的任何内容，只能暂停和恢复音频。我可能没有正确搜索。

如果重要，以下是我目前如何制作音频：

AudioInputStream stream = AudioSystem.getAudioInputStream("...file...");
AudioFormat format = stream.getFormat();
SourceDataLine.Info info = new DataLine.Info(SourceDataLine.class, format,((int)stream.getFrameLength()*format.getFrameSize()));
SourceDataLine line = (SourceDataLine)AudioSystem.getLine(info);
int bufferSize = line.getBufferSize();
byte inBuffer[] = new byte[bufferSize];
byte outBuffer[] = new byte[bufferSize];
int numRead, numWritten;
do {
numRead = audioStream.read(inBuffer, 0, bufferSize);
if(numRead <= 0) {
myAudio.flushStream();
} else {
myAudio.writeBytesToStream(inBuffer, numRead);
}
do {
numWritten = myAudio.readBytesFromStream(outBuffer, bufferSize);
if(numWritten > 0) {
line.write(outBuffer, 0, numWritten);
}
} while(numWritten > 0);
} while(numRead > 0);

Answer 1

您遇到的问题可能源于您在调整offset而不调整length.如果数组的长度为 10 个字节，并且您开始从偏移量 5 而不是 0 读取 10 个字节，则读取的数组末尾后 5 个字节。

我建议首先在 AudioInputStream 上使用 skip(long( 跳过适当数量的字节，然后写入该行。

AudioInputStream stream = AudioSystem.getAudioInputStream("...file...");
AudioFormat format = stream.getFormat();
// find out how many bytes you have to skip, this depends on bytes per frame (a.k.a. frameSize)
int secondsToSkip = 10;
long bytesToSkip = format.getFrameSize() * ((int)format.getFrameRate()) * secondsToSkip;
// now skip until the correct number of bytes have been skipped
int justSkipped = 0;
while (bytesToSkip > 0 && (justSkipped = stream.skip(bytesToSkip)) > 0) {
bytesToSkip -= justSkipped;
}
// then proceed with writing to your line like you have done before
[...]

请注意，这仅在音频文件未压缩的情况下有效。如果您正在处理类似.mp3，您首先必须将流转换为 PCM(请参阅 https://stackoverflow.com/a/41850901/942774(

Answer 2

我创建了一个编译和工作的示例。 您可以从任何时间点播放.wav文件。 它也应该适用于 mp3 文件，但我还没有测试过。 为此调用 mp3ToWav((。

import javax.sound.sampled.*;
import java.io.File;
import java.io.IOException;
public class PlayWavAtTimePoint {
public static void main(String[] args) throws Exception {
String fileName = args[0];
int secondsToSkip = (Integer.parseInt(args[1]));
PlayWavAtTimePoint program = new PlayWavAtTimePoint();
AudioInputStream is = program.getAudioInputStream(fileName);
program.skipFromBeginning(is, secondsToSkip);
program.playSound(is);
}
private static void skipFromBeginning(AudioInputStream audioStream, int secondsToSkip) throws UnsupportedAudioFileException, IOException, LineUnavailableException {
AudioFormat format = audioStream.getFormat();
// find out how many bytes you have to skip, this depends on bytes per frame (a.k.a. frameSize)
long bytesToSkip = format.getFrameSize() * ((int)format.getFrameRate()) * secondsToSkip;

// now skip until the correct number of bytes have been skipped
long justSkipped = 0;
while (bytesToSkip > 0 && (justSkipped = audioStream.skip(bytesToSkip)) > 0) {
bytesToSkip -= justSkipped;
}
}

private static final int BUFFER_SIZE = 128000;

/**
* @param filename the name of the file that is going to be played
*/
public void playSound(String filename) throws IOException, UnsupportedAudioFileException, LineUnavailableException {
AudioInputStream audioStream = getAudioInputStream(filename);
playSound(audioStream);
}
private AudioInputStream getAudioInputStream(String filename) throws UnsupportedAudioFileException, IOException {
return AudioSystem.getAudioInputStream(new File(filename));
}
public void playSound(AudioInputStream audioStream) throws LineUnavailableException, IOException {
AudioFormat audioFormat = audioStream.getFormat();
DataLine.Info info = new DataLine.Info(SourceDataLine.class, audioFormat);
SourceDataLine audioOutput = (SourceDataLine) AudioSystem.getLine(info);
audioOutput.open(audioFormat);
audioOutput.start();
//This seems to be reading the whole file into a buffer before playing ... not efficient.
//Why not stream it?
int nBytesRead = 0;
byte[] abData = new byte[BUFFER_SIZE];
while (nBytesRead != -1) {
nBytesRead = audioStream.read(abData, 0, abData.length);
if (nBytesRead >= 0) {
audioOutput.write(abData, 0, nBytesRead);
}
}
audioOutput.drain();
audioOutput.close();
}
/**
* Invoke this function to convert to a playable file.
*/
public static void mp3ToWav(File mp3Data) throws UnsupportedAudioFileException, IOException {
// open stream
AudioInputStream mp3Stream = AudioSystem.getAudioInputStream(mp3Data);
AudioFormat sourceFormat = mp3Stream.getFormat();
// create audio format object for the desired stream/audio format
// this is *not* the same as the file format (wav)
AudioFormat convertFormat = new AudioFormat(AudioFormat.Encoding.PCM_SIGNED,
sourceFormat.getSampleRate(), 16,
sourceFormat.getChannels(),
sourceFormat.getChannels() * 2,
sourceFormat.getSampleRate(),
false);
// create stream that delivers the desired format
AudioInputStream converted = AudioSystem.getAudioInputStream(convertFormat, mp3Stream);
// write stream into a file with file format wav
AudioSystem.write(converted, AudioFileFormat.Type.WAVE, new File("/tmp/out.wav"));
}
}