/*
 Implementation of LiveSoundInterface actor that in dependent on javax.

 Copyright (c) 2011-2014 The Regents of the University of California.
 All rights reserved.
 Permission is hereby granted, without written agreement and without
 license or royalty fees, to use, copy, modify, and distribute this
 software and its documentation for any purpose, provided that the above
 copyright notice and the following two paragraphs appear in all copies
 of this software.

 IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
 FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
 ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
 THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
 SUCH DAMAGE.

 THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
 PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
 CALIFORNIA HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
 ENHANCEMENTS, OR MODIFICATIONS.

 PT_COPYRIGHT_VERSION_2
 COPYRIGHTENDKEY
 */

package ptolemy.media.javasound;

import java.io.IOException;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioFormat.Encoding;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.DataLine;
import javax.sound.sampled.LineUnavailableException;
import javax.sound.sampled.SourceDataLine;
import javax.sound.sampled.TargetDataLine;

///////////////////////////////////////////////////////////////////
//// LiveSoundJavaSE

/**
 Implementation of LiveSoundInterface that in dependent on javax.
 This actor sequentially outputs audio samples that are captured
 from the audio input port of the computer. The audio input port
 typically corresponds to either the microphone input, line-in,
 or cd audio from the cdrom or dvd drive. It is not possible to
 select the desired input port under Java. This must be done from
 the operating system. This actor should be fired often enough to
 prevent overflow of the internal audio capture buffer.
 Overflow should be avoided, since it will result in loss of
 data. Each captured audio sample is converted to a double that
 may range from -1.0 to 1.0. Thus, the output type of this actor
 is DoubleToken.


 @author Brian K. Vogel and Neil E. Turner and Steve Neuendorffer, Edward A. Lee, Contributor: Dennis Geurts, Ishwinder Singh
 @version $Id: LiveSoundJavaSE.java 70402 2014-10-23 00:52:20Z cxh $
 @since Ptolemy II 10.0
 @Pt.ProposedRating Red (ishwinde)
 @Pt.AcceptedRating Red (ishwinde)
 */
public class LiveSoundJavaSE extends LiveSoundCommon implements
LiveSoundInterface {

    /** Flush queued data from the capture buffer.  The flushed data is
     *  discarded.  It is only legal to flush the capture buffer after
     *  startCapture() is called.  Flushing an active audio buffer is likely to
     *  cause a discontinuity in the data, resulting in a perceptible click.
     *  <p>
     *  Note that only the object with the exclusive lock on the capture audio
     *  resources is allowed to invoke this method. An exception will occur if
     *  the specified object does not have the lock on the playback audio
     *  resources.
     *
     *  @param consumer The object that has an exclusive lock on
     *   the capture audio resources.
     *
     *  @exception IllegalStateException If audio capture is currently
     *  inactive. That is, if startCapture() has not yet been called
     *  or if stopCapture() has already been called.
     *
     *  @exception IOException If the calling program does not have permission
     *  to access the audio capture resources.
     */
    @Override
    public void flushCaptureBuffer(Object consumer) throws IOException,
    IllegalStateException {
        if (!isCaptureActive()) {
            throw new IllegalStateException("Object: " + consumer.toString()
                    + " attempted to call LiveSound.flushCaptureBuffer(), but "
                    + "capture is inactive.  Try to startCapture().");
        }

        if (!_soundConsumers.contains(consumer)) {
            throw new IOException("Object: " + consumer.toString()
                    + " attempted to call LiveSound.flushCaptureBuffer(), but "
                    + "this object does not have permission to access the "
                    + "audio capture resource.");
        }
        _flushCaptureBuffer();
    }

    /** Flush queued data from the playback buffer.  The flushed data is
     *  discarded.  It is only legal to flush the playback buffer after
     *  startPlayback() is called, and only makes sense to do so (but is
     *  not required) after putSamples() is called.  Flushing an active audio
     *  buffer is likely to cause a discontinuity in the data, resulting in a
     *  perceptible click.
     *  <p>
     *  Note that only the object with the exclusive lock on the playback audio
     *  resources is allowed to invoke this method. An exception will occur if
     *  the specified object does not have the lock on the playback audio
     *  resources.
     *
     *  @param producer The object that has an exclusive lock on
     *   the playback audio resources.
     *
     *  @exception IllegalStateException If audio playback is currently
     *  inactive. That is, if startPlayback() has not yet been called
     *  or if stopPlayback() has already been called.
     *
     *  @exception IOException If the calling program does not have permission
     *  to access the audio playback resources.
     */
    @Override
    public void flushPlaybackBuffer(Object producer) throws IOException,
    IllegalStateException {
        _flushPlaybackBuffer();
    }

    /** Return the number of bits per audio sample, which is
     *  set by the setBitsPerSample() method. The default
     *  value of this parameter is 16 bits.
     *
     * @return The sample size in bits.
     * @see #setBitsPerSample(int)
     */

    /** Return the size of the internal capture audio buffer, in samples per
     *  channel.
     *
     *  @return The internal buffer size in samples per channel.
     *
     *  @exception IllegalStateException If audio capture is inactive.
     */
    @Override
    public int getBufferSizeCapture() throws IllegalStateException {
        if (_targetLine != null) {
            return _targetLine.getBufferSize() / (_bytesPerSample * _channels);
        } else {
            throw new IllegalStateException("LiveSound: "
                    + "getBufferSizeCapture(), capture is probably inactive."
                    + "Try to startCapture().");
        }
    }

    /** Return the size of the internal playback audio buffer, in samples per
     *  channel. This may differ from the requested buffer size if the hardware
     *  does not support the requested buffer size. If playback has not
     *  been started, then will simply return the requested buffer size.
     *  @return The internal buffer size in samples per channel.
     *  @exception IllegalStateException If audio playback is inactive.
     */
    @Override
    public int getBufferSizePlayback() {
        if (_sourceLine != null) {
            return _sourceLine.getBufferSize() / (_bytesPerSample * _channels);
        } else {
            return _bufferSize;
        }
    }

    /** Return an array of captured audio samples. This method
     *  should be repeatedly called to obtain audio data.
     *  The returned audio samples will have values in the range
     *  [-1, 1], regardless of the audio bit resolution (bits per
     *  sample).  This method should be called often enough to
     *  prevent overflow of the internal audio buffer. If
     *  overflow occurs, some audio data will be lost but no
     *  exception or other error condition will occur. If
     *  the audio data is not yet available, then this method
     *  will block until the data is available.
     *  <p>
     *  The first index of the returned array
     *  represents the channel number (0 for first channel, 1 for
     *  second channel). The number of channels is set by the
     *  setChannels() method. The second index represents the
     *  sample index within a channel. For example,
     *  <i>returned array</i>[n][m] contains the (m+1)th sample
     *  of the (n+1)th channel. For each channel, n, the length of
     *  <i>returned array</i>[n] is equal to the value returned by
     *  the getTransferSize() method.
     *  The size of the 2nd dimension of the returned array
     *  is set by the setTransferSize() method.
     *  <p>
     *  Note that only the object with the exclusive lock on
     *  the captured audio resources is allowed to invoked this
     *  method. An exception will occur if the specified object
     *  does not have the lock on the captured audio resources.
     *
     *  @param consumer The object that has an exclusive lock on
     *   the capture audio resources.
     *
     *  @return Two dimensional array of captured audio samples.
     *
     *  @exception IllegalStateException If audio capture is currently
     *   inactive.  That is, if startCapture() has not yet been called or if
     *   stopCapture() has already been called.
     *
     *  @exception IOException If the calling program does not have permission
     *   to access the audio capture resources.
     */
    @Override
    public double[][] getSamples(Object consumer) throws IOException,
    IllegalStateException {
        if (!isCaptureActive()) {
            throw new IllegalStateException("Object: " + consumer.toString()
                    + " attempted to call LiveSound.getSamples(), but "
                    + "capture is inactive.  Try to startCapture().");
        }

        if (!_soundConsumers.contains(consumer)) {
            throw new IOException("Object: " + consumer.toString()
                    + " attempted to call LiveSound.getSamples(), but "
                    + "this object does not have permission to access the "
                    + "audio capture resource.");
        }

        // Real-time capture.
        int numBytesRead = _targetLine.read(_captureData, 0,
                _captureData.length);

        // Check if we need to reallocate.
        if (_channels != _audioInDoubleArray.length
                || _transferSize != _audioInDoubleArray[0].length) {
            // Reallocate
            _audioInDoubleArray = new double[_channels][_transferSize];
        }

        if (numBytesRead == _captureData.length) {
            // Convert byte array to double array.
            _byteArrayToDoubleArray(_audioInDoubleArray, _captureData);
            return _audioInDoubleArray;
        } else {
            throw new IOException("Failed to capture correct number of bytes");
        }
    }

    /** Play an array of audio samples. There will be a
     *  delay before the audio data is actually heard, since the
     *  audio data in <i>samplesArray</i> is queued to an
     *  internal audio buffer. The setBufferSize() method suggests a size
     *  for the internal buffer. An upper bound
     *  on the latency is given by (<i>bufferSize</i> /
     *  <i>sampleRate</i>) seconds. This method should be invoked often
     *  enough to prevent underflow of the internal audio buffer.
     *  Underflow is undesirable since it will cause audible gaps
     *  in audio playback, but no exception or error condition will
     *  occur. If the caller attempts to write more data than can
     *  be written, this method blocks until the data can be
     *  written to the internal audio buffer.
     *  <p>
     *  The samples should be in the range (-1, 1). Samples that are
     *  outside this range will be hard-clipped so that they fall
     *  within this range.
     *  <p>
     *  The first index of the specified array
     *  represents the channel number (0 for first channel, 1 for
     *  second channel, etc.). The number of channels is set by the
     *  setChannels() method. The second index represents the
     *  sample index within a channel. For example,
     *  putSamplesArray[n][m] contains the (m+1)th sample
     *  of the (n+1)th channel.
     *  <p>
     *  Note that only the object with the exclusive lock on
     *  the playback audio resources is allowed to invoke this
     *  method. An exception will occur if the specified object
     *  does not have the lock on the playback audio resources.
     *
     *  @param producer The object that has an exclusive lock on
     *   the playback audio resources.
     *
     *  @param samplesArray A two dimensional array containing
     *  the samples to play or write to a file.
     *
     *  @exception IOException If the calling program does not have permission
     *  to access the audio playback resources.
     *
     *  @exception IllegalStateException If audio playback is currently
     *  inactive. That is, If startPlayback() has not yet been called
     *  or if stopPlayback() has already been called.
     */
    @Override
    public void putSamples(Object producer, double[][] samplesArray)
            throws IOException, IllegalStateException {
        if (!isPlaybackActive()) {
            throw new IllegalStateException("Object: " + producer.toString()
                    + " attempted to call LiveSound.putSamples(), but "
                    + "playback is inactive.  Try to startPlayback().");
        }
        // Convert array of double valued samples into
        // the proper byte array format.
        byte[] playbackData = _doubleArrayToByteArray(samplesArray);

        // Now write the array to output device.
        int written = _sourceLine.write(playbackData, 0, playbackData.length);

        if (written != playbackData.length) {
            System.out.println("dropped samples!");
        }
    }

    /** Stop audio capture. If audio capture is already inactive,
     *  then do nothing. This method should generally not be used,
     *  but it may be needed to turn of audio capture for the
     *  case where an ill-behaved application exits without calling
     *  stopCapture(). The preferred way of stopping audio capture
     *  is by calling the stopCapture() method.
     *
     */
    @Override
    public void resetCapture() {
        if (_targetLine != null) {
            if (_targetLine.isOpen() == true) {
                _targetLine.stop();
                _targetLine.close();
                _targetLine = null;
            }
        }

        _captureIsActive = false;
    }

    /** Stop audio playback. If audio playback is already inactive,
     *  then do nothing. This method should generally not be used,
     *  but it may be needed to turn of audio playback for the
     *  case where an ill-behaved application exits without calling
     *  stopPlayback(). The preferred way of stopping audio playback
     *  is by calling the stopPlayback() method.
     *
     */
    @Override
    public void resetPlayback() {
        _stopPlayback();
        _playbackIsActive = false;
    }

    /** Set the number of bits per sample to use for audio capture
     *  and playback and notify any registered listeners of the change.
     *  Allowable values include 8 and 16 bits. If
     *  this method is not invoked, then the default value of 16
     *  bits is used.
     *  @param bitsPerSample The number of bits per sample.
     *  @exception IOException If the specified bits per sample is
     *   not supported by the audio hardware or by Java.
     *  @see #getBitsPerSample()
     */
    @Override
    public void setBitsPerSample(int bitsPerSample) throws IOException {
        _bitsPerSample = bitsPerSample;
        // FIXME: The following is wrong. Probably should just set bytes per sample.
        _bytesPerSample = _bitsPerSample / 8;
        // Note: _maxSample is maximum positive number, which ensures
        // that maximum negative number is also in range.
        switch (_bytesPerSample) {
        case 1:
            _maxSampleReciprocal = 1.0 / 128;
            _maxSample = 127;
            break;
        case 2:
            _maxSampleReciprocal = 1.0 / 32768;
            _maxSample = 32767;
            break;
        case 3:
            _maxSampleReciprocal = 1.0 / 8388608;
            _maxSample = 8388607;
            break;
        case 4:
            _maxSampleReciprocal = 1.0 / 147483648e9;
            _maxSample = 147483647e9;
            break;
        default:
            // Should not happen.
            _maxSampleReciprocal = 0;
        }

        if (_captureIsActive && _playbackIsActive) {
            // Restart capture/playback with new bitsPerSample.
            _stopCapture();
            _stopPlayback();
            _startCapture();
            _startPlayback();
        } else if (_captureIsActive) {
            // Restart capture with new bitsPerSample.
            _stopCapture();
            _startCapture();
        } else if (_playbackIsActive) {
            // Restart playback with new bitsPerSample.
            _stopPlayback();
            _startPlayback();
        }

        // Notify listeners of the change.
        _notifyLiveSoundListeners(LiveSoundEvent.BITS_PER_SAMPLE);
    }

    /** Request that the internal capture and playback
     *  audio buffers have bufferSize samples per channel and notify the
     *  registered listeners of the change. If this method
     *  is not invoked, the default value of 1024 is used.
     *
     *  @param bufferSize The suggested size of the internal capture and
     *   playback audio buffers, in samples per channel.
     *  @exception IOException If the specified number of channels is
     *   not supported by the audio hardware or by Java.
     *  @see #getBufferSize()
     */
    @Override
    public void setBufferSize(int bufferSize) throws IOException {
        _bufferSize = bufferSize;
        if (_captureIsActive && _playbackIsActive) {
            // Restart capture/playback with new bufferSize.
            _stopCapture();
            _stopPlayback();
            _startCapture();
            _startPlayback();
        } else if (_captureIsActive) {
            // Restart capture with new bufferSize.
            _stopCapture();
            _startCapture();
        } else if (_playbackIsActive) {
            // Restart playback with new bufferSize.
            _stopPlayback();
            _startPlayback();
        }
        // Notify listeners of the change.
        _notifyLiveSoundListeners(LiveSoundEvent.BUFFER_SIZE);
    }

    /** Set the number of audio channels to use for capture and
     *  playback and notify any registered listeners of the change.
     *  Allowable values are 1 (for mono) and 2 (for
     *  stereo). If this method is not invoked, the default
     *  value of 1 audio channel is used. Note that this method
     *  sets the size of the first dimension of the
     *  2-dimensional array used by the putSamples() and
     *  getSamples() methods.
     *
     *  @param channels The number audio channels.
     *
     *  @exception IOException If the specified number of channels is
     *   not supported by the audio hardware or by Java.
     *  @see #getChannels()
     */
    @Override
    public void setChannels(int channels) throws IOException {
        _channels = channels;
        if (_captureIsActive && _playbackIsActive) {
            // Restart capture/playback with new number of channels.
            _stopCapture();
            _stopPlayback();
            _startCapture();
            _startPlayback();
        } else if (_captureIsActive) {
            // Restart capture with new number of channels.
            _stopCapture();
            _startCapture();
        } else if (_playbackIsActive) {
            // Restart playback with new number of channels.
            _stopPlayback();
            _startPlayback();
        }
        // Notify listeners of the change.
        _notifyLiveSoundListeners(LiveSoundEvent.CHANNELS);
    }

    /** Set the sample rate to use for audio capture and playback
     *  and notify an registered listeners of the change.
     *  Allowable values for this parameter are 8000, 11025,
     *  22050, 44100, and 48000 Hz. If this method is not invoked,
     *  then the default value of 8000 Hz is used.
     *
     *  @param sampleRate Sample rate in Hz.
     *
     *  @exception IOException If the specified sample rate is
     *   not supported by the audio hardware or by Java.
     *  @see #getSampleRate()
     */
    @Override
    public void setSampleRate(int sampleRate) throws IOException {
        _sampleRate = sampleRate;
        if (_captureIsActive && _playbackIsActive) {
            // Restart capture/playback with new sample rate.
            _stopCapture();
            _stopPlayback();
            _startCapture();
            _startPlayback();
        } else if (_captureIsActive) {
            // Restart capture with new sample rate.
            _stopCapture();
            _startCapture();
        } else if (_playbackIsActive) {
            // Restart playback with new sample rate.
            _stopPlayback();
            _startPlayback();
        }
        // Notify listeners of the change.
        _notifyLiveSoundListeners(LiveSoundEvent.SAMPLE_RATE);
    }

    /** Start audio capture. The specified object will be
     *  given an exclusive lock on the audio capture resources
     *  until the stopCapture() method is called with the
     *  same object reference. After this method returns,
     *  the getSamples() method may be repeatedly invoked
     *  (using the object reference as a parameter) to
     *  capture audio.
     *  <p>
     *  If audio capture is already active, then an
     *  exception will occur.
     *
     *  @param consumer The object to be given exclusive access
     *   to the captured audio resources.
     *
     *  @exception IOException If another object currently has access
     *   to the audio capture resources or if starting the capture or
     *   playback throws it.
     *
     *  @exception IllegalStateException If this method is called
     *   while audio capture is already active.
     */
    @Override
    public void startCapture(Object consumer) throws IOException,
    IllegalStateException {
        // FIXME: consider allowing several object to
        // share the captured audio resources.
        if (_soundConsumers.size() > 0) {
            throw new IOException("Object: " + consumer.toString()
                    + " is not allowed to start audio capture because "
                    + "another object currently has access to the audio "
                    + "capture resources.");
        }

        if (!_soundConsumers.contains(consumer)) {
            _soundConsumers.add(consumer);
        } else {
            throw new IllegalStateException("Object: " + consumer.toString()
                    + " attempted to call LiveSound.startCapture() while "
                    + "audio capture was active.");
        }
        // This is a workaround for a javasound bug. In javasound,
        // when doing simultaneous capture and playback, the
        // capture process must be started first. So, if
        // there is already a playback process running then
        // stop it before starting capture.
        if (isPlaybackActive()) {
            _stopPlayback();
            _startCapture();
            _startPlayback();
        } else {
            _startCapture();
        }

        _captureIsActive = true;
    }

    /** Start audio playback. The specified object will be
     *  given an exclusive lock on the audio playback resources
     *  until the stopPlayback() method is called with the
     *  same object reference. After this method returns,
     *  the putSamples() method may be repeatedly invoked
     *  (using the object reference as a parameter) to
     *  playback audio.
     *  <p>
     *  If audio playback is already active, then an
     *  exception will occur.
     *
     *  @param producer The object to be given exclusive access
     *   to the playback resources.
     *
     *  @exception IOException If another object currently has access
     *   to the audio capture resources or if starting the playback throws it.
     *
     *  @exception IllegalStateException If this method is called
     *   while audio playback is already active.
     */
    @Override
    public void startPlayback(Object producer) throws IOException,
    IllegalStateException {
        if (!_playbackIsActive) {
            _startPlayback();
            _playbackIsActive = true;
        }
    }

    /** Stop audio capture. If the specified object has
     *  the lock on audio capture when this method is
     *  invoked, then stop audio capture. Otherwise
     *  an exception will occur.
     *
     *  @param consumer The object that held on exclusive
     *   lock on the captured audio resources when this
     *   method was invoked.
     *
     *  @exception IOException If another object currently has access
     *   to the audio capture resources or if stopping the capture throws it.
     *
     *  @exception IllegalStateException If the specified
     *   object did not hold an exclusive lock on the
     *   captured audio resources when this method was invoked.
     */
    @Override
    public void stopCapture(Object consumer) throws IOException,
    IllegalStateException {
        if (_soundConsumers.contains(consumer)) {
            _soundConsumers.remove(consumer);
        } else {
            throw new IOException("Object: " + consumer.toString()
                    + " attempted to call LiveSound.stopCapture(), but "
                    + "never called LiveSound.startCapture().");
        }

        // Free up audio system resources.
        _stopCapture();
        _captureIsActive = false;
    }

    /** Stop audio playback. If the specified object has
     *  the lock on audio playback when this method is
     *  invoked, then stop audio playback. Otherwise
     *  an exception will occur.
     *
     *  @param producer The object that held on exclusive
     *   lock on the playback audio resources when this
     *   method was invoked.
     *
     *  @exception IOException If another object currently has access
     *   to the audio capture resources or if stopping the playback throws it.

     *  @exception IllegalStateException If the specified
     *   object did not hold an exclusive lock on the
     *   playback audio resources when this method was invoked.
     *
     */
    @Override
    public void stopPlayback(Object producer) throws IOException,
    IllegalStateException {
        if (_playbackIsActive) {
            _stopPlayback();
        }
        _playbackIsActive = false;
    }

    ///////////////////////////////////////////////////////////////////
    ////                         private methods                   ////

    /** Return a string that describes the possible encodings for an
     *  AudioFormat.
     *  @param format The audio format.
     *  @return A string describing the audio formats available.
     */
    private String _encodings(AudioFormat format) {
        // Print out the possible encodings
        AudioFormat.Encoding[] encodings = AudioSystem
                .getTargetEncodings(format);
        StringBuffer encodingDescriptions = new StringBuffer();
        for (Encoding encoding : encodings) {
            encodingDescriptions.append(encoding + "\n");
            AudioFormat[] formats = AudioSystem.getTargetFormats(encoding,
                    format);
            for (AudioFormat format2 : formats) {
                encodingDescriptions.append("  " + format2 + "\n");
            }
        }
        return encodingDescriptions.toString();
    }

    private void _flushCaptureBuffer() {
        _targetLine.flush();
    }

    private void _flushPlaybackBuffer() {
        _sourceLine.flush();
    }

    /** Start audio capture.
     */
    private void _startCapture() throws IOException {
        boolean signed = true;
        boolean bigEndian = true;
        AudioFormat format = new AudioFormat(_sampleRate, _bitsPerSample,
                _channels, signed, bigEndian);

        DataLine.Info targetInfo = new DataLine.Info(TargetDataLine.class,
                format, AudioSystem.NOT_SPECIFIED);

        try {
            _targetLine = (TargetDataLine) AudioSystem.getLine(targetInfo);

            // Note: 2nd parameter is the buffer size (in bytes).
            // Larger values increase latency but may be required if
            // garbage collection, etc. is an issue.
            _targetLine.open(format, _bufferSize * _bytesPerSample * _channels);
        } catch (IllegalArgumentException ex) {
            IOException exception = new IOException(
                    "Incorrect argument, possible encodings for\n" + format
                    + "\n are:\n" + _encodings(format));
            exception.initCause(ex);
            throw exception;
        } catch (LineUnavailableException ex2) {
            throw new IOException("Unable to open the line for "
                    + "real-time audio capture: " + ex2);
        }

        // Array of audio samples in byte format.
        _captureData = new byte[_transferSize * _bytesPerSample * _channels];
        _audioInDoubleArray = new double[_channels][_transferSize];

        // Start the target data line
        _targetLine.start();
    }

    /** Start audio playback.
     */
    private void _startPlayback() throws IOException {
        boolean signed = true;
        boolean bigEndian = true;

        AudioFormat format = new AudioFormat(_sampleRate, _bitsPerSample,
                _channels, signed, bigEndian);

        // As of Java 5.0, no longer need to specify this.
        // Use the convenience method AudioSystem.getSourceDataLine(AudioFormat).
        // DataLine.Info sourceInfo = new DataLine.Info(SourceDataLine.class,
        //        format, AudioSystem.NOT_SPECIFIED);

        // Get and open the source data line for playback.
        try {
            // Source DataLine is really a target for
            // audio data, not a source.
            _sourceLine = AudioSystem.getSourceDataLine(format);

            // Open line and suggest a buffer size (in bytes) to use or
            // the internal audio buffer.
            _sourceLine.open(format, _bufferSize * _bytesPerSample * _channels);
        } catch (IllegalArgumentException ex) {
            IOException exception = new IOException(
                    "Incorrect argument, possible encodings for\n" + format
                    + "\n are:\n" + _encodings(format));
            exception.initCause(ex);
            throw exception;
        } catch (LineUnavailableException ex) {
            throw new IOException("Unable to open the line for "
                    + "real-time audio playback: " + ex);
        }
        // Start the source data line
        _sourceLine.start();
    }

    /** Stop audio playback.
     */
    private void _stopPlayback() {
        if (_sourceLine != null) {
            _sourceLine.drain();
            _sourceLine.stop();
            _sourceLine.close();
        }

        _sourceLine = null;
    }

    /** Stop audio capture.
     */
    private void _stopCapture() {
        if (_targetLine != null) {
            if (_targetLine.isOpen() == true) {
                _targetLine.stop();
                _targetLine.close();
                _targetLine = null;
            }
        }
    }

    ///////////////////////////////////////////////////////////////////
    ////                         private variables                 ////

    /** Interface to the hardware for reading data. */
    private SourceDataLine _sourceLine;

    /** Interface to the hardware for producing sound. */
    private TargetDataLine _targetLine;

}