layeridecoder.java

java处理声音文件

/*
 * 12/12/99		Initial version. Adapted from javalayer.java
 *				and Subband*.java. [e-mail]
/*-----------------------------------------------------------------------
 *  This program 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 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *----------------------------------------------------------------------
 */


package javazoom.jl.decoder;

/**
 * Implements decoding of MPEG Audio Layer I frames. 
 */

class LayerIDecoder implements FrameDecoder
{
	protected Bitstream 			stream;
    protected Header 				header;
    protected SynthesisFilter 		filter1, filter2;
    protected Obuffer 				buffer;
    protected int 					which_channels;
	protected int					mode;
	
	protected int					num_subbands;
	protected Subband[]				subbands;
	protected Crc16[]				crc	= null;	// new Crc16[1] to enable CRC checking.
	
	public LayerIDecoder()
	{
	}
	
	public void create(Bitstream stream0, Header header0,
		SynthesisFilter filtera, SynthesisFilter filterb,
		Obuffer buffer0, int which_ch0)
	{		
	  	stream         = stream0;
	  	header         = header0;
	  	filter1        = filtera;
	  	filter2        = filterb;
	  	buffer         = buffer0;
	  	which_channels = which_ch0;
		
	}
	
	
	
	public void decodeFrame()
	{
		
		num_subbands = header.number_of_subbands();
		subbands = new Subband[32];
		mode = header.mode();
		
		createSubbands();
		
		readAllocation();
		readScaleFactorSelection();
		
	    if ((crc != null) || header.checksum_ok())
  		{
			readScaleFactors();
			
			readSampleData();			
		}

	}

	protected void createSubbands()
	{  		
		int i;
		if (mode == Header.SINGLE_CHANNEL)
  		  for (i = 0; i < num_subbands; ++i)
  		    subbands[i] = new SubbandLayer1(i);
  		else if (mode == Header.JOINT_STEREO)
		{
  		  for (i = 0; i < header.intensity_stereo_bound(); ++i)
  		    subbands[i] = new SubbandLayer1Stereo(i);
  		  for (; i < num_subbands; ++i)
  		    subbands[i] = new SubbandLayer1IntensityStereo(i);
  		}
		else
		{
  		  for (i = 0; i < num_subbands; ++i)
  		    subbands[i] = new SubbandLayer1Stereo(i);
  	    }		
	}
	
	protected void readAllocation()
	{
		// start to read audio data:
  	    for (int i = 0; i < num_subbands; ++i)
  	      subbands[i].read_allocation(stream, header, crc[0]);
		
	}

	protected void readScaleFactorSelection()
	{
		// scale factor selection not present for layer I. 
	}
	
	protected void readScaleFactors()
	{
		for (int i = 0; i < num_subbands; ++i)
  		  subbands[i].read_scalefactor(stream, header);  		
	}
	
	protected void readSampleData()
	{
		boolean read_ready = false;
		boolean write_ready = false;
		int mode = header.mode();
		int i;
		do
  		{
  		  for (i = 0; i < num_subbands; ++i)
  		  	read_ready = subbands[i].read_sampledata(stream);
  		  do
  		  {
  		  	for (i = 0; i < num_subbands; ++i)
  		  		write_ready = subbands[i].put_next_sample(which_channels,filter1, filter2);

  		  	filter1.calculate_pcm_samples(buffer);
  		  	if ((which_channels == OutputChannels.BOTH_CHANNELS) && (mode != Header.SINGLE_CHANNEL))
           		filter2.calculate_pcm_samples(buffer);
  		  } while (!write_ready);
  		} while (!read_ready);
		
	}

	/**
	 * Abstract base class for subband classes of layer I and II
	 */
	static abstract class Subband
	{
	 /*
	  *  Changes from version 1.1 to 1.2:
	  *    - array size increased by one, although a scalefactor with index 63
	  *      is illegal (to prevent segmentation faults)
	  */
	  // Scalefactors for layer I and II, Annex 3-B.1 in ISO/IEC DIS 11172:
	  public static final float scalefactors[] =
	  {
	  2.00000000000000f, 1.58740105196820f, 1.25992104989487f, 1.00000000000000f,
	  0.79370052598410f, 0.62996052494744f, 0.50000000000000f, 0.39685026299205f,
	  0.31498026247372f, 0.25000000000000f, 0.19842513149602f, 0.15749013123686f,
	  0.12500000000000f, 0.09921256574801f, 0.07874506561843f, 0.06250000000000f,
	  0.04960628287401f, 0.03937253280921f, 0.03125000000000f, 0.02480314143700f,
	  0.01968626640461f, 0.01562500000000f, 0.01240157071850f, 0.00984313320230f,
	  0.00781250000000f, 0.00620078535925f, 0.00492156660115f, 0.00390625000000f,
	  0.00310039267963f, 0.00246078330058f, 0.00195312500000f, 0.00155019633981f,
	  0.00123039165029f, 0.00097656250000f, 0.00077509816991f, 0.00061519582514f,
	  0.00048828125000f, 0.00038754908495f, 0.00030759791257f, 0.00024414062500f,
	  0.00019377454248f, 0.00015379895629f, 0.00012207031250f, 0.00009688727124f,
	  0.00007689947814f, 0.00006103515625f, 0.00004844363562f, 0.00003844973907f,
	  0.00003051757813f, 0.00002422181781f, 0.00001922486954f, 0.00001525878906f,
	  0.00001211090890f, 0.00000961243477f, 0.00000762939453f, 0.00000605545445f,
	  0.00000480621738f, 0.00000381469727f, 0.00000302772723f, 0.00000240310869f,
	  0.00000190734863f, 0.00000151386361f, 0.00000120155435f, 0.00000000000000f /* illegal scalefactor */
	  };

	  public abstract void read_allocation (Bitstream stream, Header header, Crc16 crc);
	  public abstract void read_scalefactor (Bitstream stream, Header header);
	  public abstract boolean read_sampledata (Bitstream stream);
	  public abstract boolean put_next_sample (int channels, SynthesisFilter filter1, SynthesisFilter filter2);
	};
	
	/**
	 * Class for layer I subbands in single channel mode.
	 * Used for single channel mode
	 * and in derived class for intensity stereo mode
	 */
	static class SubbandLayer1 extends Subband
	{

	  // Factors and offsets for sample requantization
	  public static final float table_factor[] = {
	   0.0f, (1.0f/2.0f) * (4.0f/3.0f), (1.0f/4.0f) * (8.0f/7.0f), (1.0f/8.0f) * (16.0f/15.0f),
	  (1.0f/16.0f) * (32.0f/31.0f), (1.0f/32.0f) * (64.0f/63.0f), (1.0f/64.0f) * (128.0f/127.0f),
	  (1.0f/128.0f) * (256.0f/255.0f), (1.0f/256.0f) * (512.0f/511.0f),
	  (1.0f/512.0f) * (1024.0f/1023.0f), (1.0f/1024.0f) * (2048.0f/2047.0f),
	  (1.0f/2048.0f) * (4096.0f/4095.0f), (1.0f/4096.0f) * (8192.0f/8191.0f),
	  (1.0f/8192.0f) * (16384.0f/16383.0f), (1.0f/16384.0f) * (32768.0f/32767.0f)
	  };

	  public static final float table_offset[] = {
	   0.0f, ((1.0f/2.0f)-1.0f) * (4.0f/3.0f), ((1.0f/4.0f)-1.0f) * (8.0f/7.0f), ((1.0f/8.0f)-1.0f) * (16.0f/15.0f),
	  ((1.0f/16.0f)-1.0f) * (32.0f/31.0f), ((1.0f/32.0f)-1.0f) * (64.0f/63.0f), ((1.0f/64.0f)-1.0f) * (128.0f/127.0f),
	  ((1.0f/128.0f)-1.0f) * (256.0f/255.0f), ((1.0f/256.0f)-1.0f) * (512.0f/511.0f),
	  ((1.0f/512.0f)-1.0f) * (1024.0f/1023.0f), ((1.0f/1024.0f)-1.0f) * (2048.0f/2047.0f),
	  ((1.0f/2048.0f)-1.0f) * (4096.0f/4095.0f), ((1.0f/4096.0f)-1.0f) * (8192.0f/8191.0f),
	  ((1.0f/8192.0f)-1.0f) * (16384.0f/16383.0f), ((1.0f/16384.0f)-1.0f) * (32768.0f/32767.0f)
	  };

	  protected int			 subbandnumber;
	  protected int			 samplenumber;
	  protected int			 allocation;
	  protected float		 scalefactor;
	  protected int 		 samplelength;
	  protected float 		 sample;
	  protected float 		 factor, offset;

	  /**
	   * Construtor.
	   */
	  public SubbandLayer1(int subbandnumber)
	  {
	    this.subbandnumber = subbandnumber;
	    samplenumber = 0;  
	  }
	  
	  /**
	   *
	   */
	  public void read_allocation(Bitstream stream, Header header, Crc16 crc)
	  {
	    if ((allocation = stream.get_bits (4)) == 15) ;
		//	 cerr << "WARNING: stream contains an illegal allocation!\n";
		// MPEG-stream is corrupted!
		if (crc != null)
		 	crc.add_bits (allocation, 4);
	  	if (allocation != 0)
	    {
		 samplelength = allocation + 1;
		 factor = table_factor[allocation];
	     offset = table_offset[allocation];
	    }
	  }

	  /**
	   *
	   */
	  public void read_scalefactor(Bitstream stream, Header header)
	  {
	    if (allocation != 0) scalefactor = scalefactors[stream.get_bits(6)];
	  }

	  /**
	   *
	   */
	  public boolean read_sampledata(Bitstream stream)
	  {
	    if (allocation != 0)
	    {
		   sample = (float) (stream.get_bits(samplelength));
	    }
	    if (++samplenumber == 12)
	    {
		   samplenumber = 0;
		   return true;
	    }
	    return false;  
	  }

	  /**
	   *
	   */
	  public boolean put_next_sample(int channels, SynthesisFilter filter1, SynthesisFilter filter2)
	  {
	    if ((allocation !=0) && (channels != OutputChannels.RIGHT_CHANNEL))
	    {
		   float scaled_sample = (sample * factor + offset) * scalefactor;
		   filter1.input_sample (scaled_sample, subbandnumber);
	    }
	    return true;
	  }
	};
	
	/**
	 * Class for layer I subbands in joint stereo mode.
	 */
	static class SubbandLayer1IntensityStereo extends SubbandLayer1
	{
	  protected float 		channel2_scalefactor;

	  /**
	   * Constructor
	   */
	  public SubbandLayer1IntensityStereo(int subbandnumber)
	  {
		super(subbandnumber);  
	  }

	  /**
	   *
	   */
	  public void read_allocation(Bitstream stream, Header header, Crc16 crc)
	  {
	    super.read_allocation (stream, header, crc);
	  }
	  
	  /**
	   *
	   */
	  public void read_scalefactor (Bitstream stream, Header header)
	  {
	    if (allocation != 0)
	    {
		  scalefactor = scalefactors[stream.get_bits(6)];
		  channel2_scalefactor = scalefactors[stream.get_bits(6)];
	    }
	  }

	  /**
	   *
	   */
	  public boolean read_sampledata(Bitstream stream)
	  {
	  	 return super.read_sampledata (stream);
	  }
	  
	  /**
	   *
	   */
	  public boolean put_next_sample (int channels, SynthesisFilter filter1, SynthesisFilter filter2)
	  {
	    if (allocation !=0 )
	    {
	      sample = sample * factor + offset;		// requantization
		  if (channels == OutputChannels.BOTH_CHANNELS)
	      {
			float sample1 = sample * scalefactor,
			sample2 = sample * channel2_scalefactor;
			filter1.input_sample(sample1, subbandnumber);
			filter2.input_sample(sample2, subbandnumber);
		  }
		  else if (channels == OutputChannels.LEFT_CHANNEL)
		  {
			float sample1 = sample * scalefactor;
			filter1.input_sample(sample1, subbandnumber);
		  }
		  else
		  {
			float sample2 = sample * channel2_scalefactor;
			filter1.input_sample(sample2, subbandnumber);
		  }
	    }
	    return true;
	  }
	};
	
	/**
	 * Class for layer I subbands in stereo mode.
	 */
	static class SubbandLayer1Stereo extends SubbandLayer1
	{
	  protected int 		channel2_allocation;
	  protected float		channel2_scalefactor;
	  protected int 		channel2_samplelength;
	  protected float	 	channel2_sample;
	  protected float 	 	channel2_factor, channel2_offset;


	  /**
	   * Constructor
	   */
	  public SubbandLayer1Stereo(int subbandnumber)
	  {
	    super(subbandnumber);
	  }
	  
	  /**
	   *
	   */
	  public void read_allocation (Bitstream stream, Header header, Crc16 crc)
	  {
	 	 allocation = stream.get_bits(4);
	     channel2_allocation = stream.get_bits(4);
	     if (crc != null)
	     {
		   crc.add_bits (allocation, 4);
	       crc.add_bits (channel2_allocation, 4);
	     }
	     if (allocation != 0)
	     {
		    samplelength = allocation + 1;
	        factor = table_factor[allocation];
	        offset = table_offset[allocation];
	     }
	     if (channel2_allocation != 0)
	     {
	        channel2_samplelength = channel2_allocation + 1;
		    channel2_factor = table_factor[channel2_allocation];
		    channel2_offset = table_offset[channel2_allocation];
	     }
	  }
	  
	  /**
	   *
	   */
	  public void read_scalefactor(Bitstream stream, Header header)
	  {
	    if (allocation != 0) scalefactor = scalefactors[stream.get_bits(6)];
	    if (channel2_allocation != 0) channel2_scalefactor = scalefactors[stream.get_bits(6)];
	  }

	  /**
	   *
	   */
	  public boolean read_sampledata (Bitstream stream)
	  {
	     boolean returnvalue = super.read_sampledata(stream);
	     if (channel2_allocation != 0)
	     {
		    channel2_sample = (float) (stream.get_bits(channel2_samplelength));
	      }
	    return(returnvalue);
	  }
	  
	  /**
	   *
	   */
	  public boolean put_next_sample(int channels, SynthesisFilter filter1, SynthesisFilter filter2)
	  {
	     super.put_next_sample (channels, filter1, filter2);
	     if ((channel2_allocation != 0) && (channels != OutputChannels.LEFT_CHANNEL))
	     {
		    float sample2 = (channel2_sample * channel2_factor + channel2_offset) *
					  channel2_scalefactor;
		    if (channels == OutputChannels.BOTH_CHANNELS)
			   filter2.input_sample (sample2, subbandnumber);
		    else
			   filter1.input_sample (sample2, subbandnumber);
	     }
	     return true;
	  }
	};
	
}