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Implementations of various audio processors (e.g. multichannel conversion, volume change, ...).
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/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   * 	Redistributions of source code must retain the above copyright notice,
 * 	this list of conditions and the following disclaimer.
 *
 *   *	Redistributions in binary form must reproduce the above copyright notice,
 * 	this list of conditions and the following disclaimer in the documentation
 * 	and/or other materials provided with the distribution.
 *
 *   *	Neither the name of the University of Southampton nor the names of its
 * 	contributors may be used to endorse or promote products derived from this
 * 	software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/**
 * 
 */
package org.openimaj.audio.conversion;

import org.openimaj.audio.AudioStream;
import org.openimaj.audio.SampleChunk;
import org.openimaj.audio.processor.AudioProcessor;
import org.openimaj.audio.samples.SampleBuffer;
import org.openimaj.audio.samples.SampleBufferFactory;

/**
 *	Converts a stereo audio stream into a mono one by averaging the
 *	channels' samples and creating a mono sample set. The audio
 *	format of the stream is changed. The process() method creates new
 *	SampleChunks with a new format.
 *
 *	@author David Dupplaw ([email protected])
 *  @created 10 Jun 2011
 *	
 */
public class MultichannelToMonoProcessor extends AudioProcessor
{
	/**
	 * 	Create a processor to process chunks.
	 */
	public MultichannelToMonoProcessor()
	{
	}
	
	/**
	 *	Create a processor for the given audio stream. The output
	 *	of this audio stream will be a mono stream.
	 * 
	 *	@param a The audio stream to process.
	 */
	public MultichannelToMonoProcessor( final AudioStream a )
	{
		super( a );
		this.setFormat( this.getFormat().clone().setNumChannels( 1 ) );
	}
	
	/** 
	 *	{@inheritDoc}
	 * 	@see org.openimaj.audio.processor.AudioProcessor#process(org.openimaj.audio.SampleChunk)
	 */
	@Override
	public SampleChunk process( final SampleChunk sample )
	{
		if( sample.getFormat().getNumChannels() == 1 )
			return sample;
		
		// Get the samples.
		final SampleBuffer sb = sample.getSampleBuffer();
		final int nChannels = sample.getFormat().getNumChannels();
		
		// Create a new buffer for the mono samples.
		final SampleBuffer sb2 = SampleBufferFactory.createSampleBuffer(
			sb.getFormat().clone().setNumChannels( 1 ),
			sb.size()/nChannels );
		
		// For all the mono samples...
		for( int i = 0; i < sb2.size(); i++ )
		{
			// Accumulate the sample value 
			double acc = 0;
			for( int c = 0; c < nChannels; c++ )
				acc += sb.get(i*nChannels+c);
			
			// Store the average to the mono channel
			sb2.set( i, (int)(acc / (double)nChannels) );
		}
			
		// Update the samples in the sample chunk 
		return sb2.getSampleChunk();
	}
}