读取给定文件，返回一个1通道输入流，其中包含给定文件中两个立体声通道的混合。
/* * Created on Oct 21, 2008 * * Spectro-Edit is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 3 of the License, or * (at your option) any later version. * * Spectro-Edit is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ import java.io.File; import java.io.IOException; import java.io.InputStream;/* from nowjava.com*/ import java.util.logging.Logger; import javax.sound.sampled.AudioFileFormat; import javax.sound.sampled.AudioFormat; import javax.sound.sampled.AudioInputStream; import javax.sound.sampled.AudioSystem; import javax.sound.sampled.UnsupportedAudioFileException; public class Main{ private static final Logger logger = Logger .getLogger(AudioFileUtils.class.getName()); /** * Reads the given file, returning a 1-channel input stream containing * a mix of the two stereo channels in the given file. * * @param desiredFormat The format that the data should be in in the returned * AudioInputStream. The channels value must be 1, and the sample size in bits * must be 16. * @param file The file to read. Currently, WAV and AIFF are supported. * Future support for mp3 and ogg vorbis is planned. * @return an audio input stream with 1 channel * @throws IOException If the file can't be read * @throws UnsupportedAudioFileException If the audio system doesn't support the audio file's type * @throws IllegalArgumentException if the */ public static AudioInputStream readAsMono( final AudioFormat desiredFormat, File file) /* *来 自 时代Java公众号 */ throws UnsupportedAudioFileException, IOException { if (desiredFormat.getSampleSizeInBits() != 16) { throw new UnsupportedOperationException( "Only 16-bit samples are supported at the moment " + "(you requested " + desiredFormat.getSampleSizeInBits() + ")"); } if (desiredFormat.getChannels() != 1) { throw new UnsupportedOperationException( "Desired number of channels should be 1 " + "(you requested " + desiredFormat.getChannels() + ")"); } AudioFileFormat fileFormat = AudioSystem.getAudioFileFormat(file); if (fileFormat.getFormat().getChannels() == 1) { return AudioSystem.getAudioInputStream(desiredFormat, AudioSystem.getAudioInputStream(file)); } else if (fileFormat.getFormat().getChannels() == 2) { AudioFormat stereoDesiredFormat = new AudioFormat( desiredFormat.getEncoding(), desiredFormat.getSampleRate(), 16, 2, 4, desiredFormat.getFrameRate(), desiredFormat.isBigEndian(), desiredFormat.properties()); final AudioInputStream stereoIn = AudioSystem .getAudioInputStream(stereoDesiredFormat, AudioSystem.getAudioInputStream(file)); InputStream mixed = new InputStream() { byte[] monobuf = new byte[16384]; int offset = 0; int length = 0; long bytesRead = 0; @Override public int read() throws IOException { if (offset < length) { bytesRead++; return monobuf[offset++] & 0xff; } length = stereoIn.read(monobuf); if (length <= 0) { logger.fine("reached EOF on original input stream (read " + length + " bytes)"); return -1; } // monobuf now contains stereo samples. let's mix them down. for (int i = 0; i < length; i += 4) { int lh, ll, rh, rl; if (desiredFormat.isBigEndian()) { lh = monobuf[i + 0]; ll = monobuf[i + 1] & 0xff; rh = monobuf[i + 2]; rl = monobuf[i + 3] & 0xff; } else { lh = monobuf[i + 1]; ll = monobuf[i + 0] & 0xff; rh = monobuf[i + 3]; rl = monobuf[i + 2] & 0xff; } int left = (lh << 8 | ll); int right = (rh << 8 | rl); int mixed = (left + right) / 2; if (desiredFormat.isBigEndian()) { monobuf[(i / 2) + 1] = (byte) (mixed & 0xff); monobuf[(i / 2) + 0] = (byte) ((mixed >> 8) & 0xff); } else { monobuf[(i / 2) + 0] = (byte) (mixed & 0xff);