header.java

java实现的多媒体播放器,可以在手机上运行

/**
 *-----------------------------------------------------------------------
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library 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 Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library 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.jlme.decoder;


import java.io.IOException;

/**
 *  Description of the Class
 *@author     micah
 *@created    December 8,2001
 */
public final class Header {

  public final static int[] [] frequencies =
    {{22050,24000,16000,1},
            {44100,48000,32000,1}};

 /** Constant for LayerI version */
  public final static int LayerI = 1;

 /** Constant for LayerII version */
  public final static int LayerII = 2;

 /** Constant for LayerIII version */
  public final static int LayerIII = 3;

  /** Constant for MPEG-1 version */
  public final static int MPEG1 = 1;

  /** Description of the Field */
  public final static int STEREO = 0;

  /** Description of the Field */
  public final static int JOINT_STEREO = 1;

  /** Description of the Field */
  public final static int DUAL_CHANNEL = 2;

  /** Description of the Field */
  public final static int SINGLE_CHANNEL = 3;

  /** Description of the Field */
  public final static int FOURTYFOUR_POINT_ONE = 0;

  /** Description of the Field */
  public final static int FOURTYEIGHT = 1;

  /** Description of the Field */
  public final static int THIRTYTWO = 2;

  /** Description of the Field */
  public final static int bitrates[] [] [] = {
            {{0
    /*
     *  free format
     */
            ,32000,48000,56000,64000,80000,96000,
            112000,128000,144000,160000,176000,192000,224000,256000,0},
            {0
    /*
     *  free format
     */
            ,8000,16000,24000,32000,40000,48000,
            56000,64000,80000,96000,112000,128000,144000,160000,0},
            {0
    /*
     *  free format
     */
            ,8000,16000,24000,32000,40000,48000,
            56000,64000,80000,96000,112000,128000,144000,160000,0}},
            {{0
    /*
     *  free format
     */
            ,32000,64000,96000,128000,160000,192000,
            224000,256000,288000,320000,352000,384000,416000,448000,0},
            {0
    /*
     *  free format
     */
            ,32000,48000,56000,64000,80000,96000,
            112000,128000,160000,192000,224000,256000,320000,384000,0},
            {0
    /*
     *  free format
     */
            ,32000,40000,48000,56000,64000,80000,
            96000,112000,128000,160000,192000,224000,256000,320000,0}}
            };

  /** Description of the Field */
  public final static String bitrate_str[] [] [] = {
            {{"free format","32 kbit/s","48 kbit/s","56 kbit/s","64 kbit/s",
            "80 kbit/s","96 kbit/s","112 kbit/s","128 kbit/s","144 kbit/s",
            "160 kbit/s","176 kbit/s","192 kbit/s","224 kbit/s","256 kbit/s",
            "forbidden"},
            {"free format","8 kbit/s","16 kbit/s","24 kbit/s","32 kbit/s",
            "40 kbit/s","48 kbit/s","56 kbit/s","64 kbit/s","80 kbit/s",
            "96 kbit/s","112 kbit/s","128 kbit/s","144 kbit/s","160 kbit/s",
            "forbidden"},
            {"free format","8 kbit/s","16 kbit/s","24 kbit/s","32 kbit/s",
            "40 kbit/s","48 kbit/s","56 kbit/s","64 kbit/s","80 kbit/s",
            "96 kbit/s","112 kbit/s","128 kbit/s","144 kbit/s","160 kbit/s",
            "forbidden"}},
            {{"free format","32 kbit/s","64 kbit/s","96 kbit/s","128 kbit/s",
            "160 kbit/s","192 kbit/s","224 kbit/s","256 kbit/s","288 kbit/s",
            "320 kbit/s","352 kbit/s","384 kbit/s","416 kbit/s","448 kbit/s",
            "forbidden"},
            {"free format","32 kbit/s","48 kbit/s","56 kbit/s","64 kbit/s",
            "80 kbit/s","96 kbit/s","112 kbit/s","128 kbit/s","160 kbit/s",
            "192 kbit/s","224 kbit/s","256 kbit/s","320 kbit/s","384 kbit/s",
            "forbidden"},
            {"free format","32 kbit/s","40 kbit/s","48 kbit/s","56 kbit/s",
            "64 kbit/s","80 kbit/s","96 kbit/s","112 kbit/s","128 kbit/s",
            "160 kbit/s","192 kbit/s","224 kbit/s","256 kbit/s","320 kbit/s",
            "forbidden"}}
            };


  public static int framesize;
  public static int nSlots;
  private static int h_layer,h_protection_bit,h_bitrate_index,h_padding_bit,h_mode_extension;
  private static int h_version;
  private static int h_mode;
  private static int h_sample_frequency;
  private static int h_number_of_subbands,h_intensity_stereo_bound;
  private static byte syncmode = BitStream.INITIAL_SYNC;


  public int version() {
    return h_version;
  }

  public int layer() {
    return h_layer;
  }

  public int bitrate_index() {
    return h_bitrate_index;
  }

  public int sample_frequency() {
    return h_sample_frequency;
  }

  public int frequency() {
    return frequencies[h_version] [h_sample_frequency];
  }

  public int mode() {
    return h_mode;
  }

  public boolean padding() {
    return (h_padding_bit != 0);
  }

  public int slots() {
    return nSlots;
  }

  public int mode_extension() {
    return h_mode_extension;
  }

  public String layer_string() {
    if (h_layer==1) return "III";
    switch (h_layer) {
      case LayerI:
        return "LayerI";
      case LayerII :
        return "LayerII";
      case LayerIII:
        return "LayerIII";
    }

    return "Unknown";
	
  }

  public String bitrate_string() {
    return bitrate_str[h_version] [h_layer - 1] [h_bitrate_index];
  }

  public String sample_frequency_string() {
    switch (h_sample_frequency) {
      case THIRTYTWO:
        return "32 kHz";
      case FOURTYFOUR_POINT_ONE:
        return "44.1 kHz";
      case FOURTYEIGHT:
        return "48 kHz";
    }

    return "not set";
  }

  public String mode_string() {
    switch (h_mode) {
      case STEREO:
        return "Stereo";
      case JOINT_STEREO:
        return "Joint stereo";
      case DUAL_CHANNEL:
        return "Dual channel";
      case SINGLE_CHANNEL:
        return "Single channel";
    }

    return "not set";
  }

  public int number_of_subbands() {
    return h_number_of_subbands;
  }

  public int intensity_stereo_bound() {
    return h_intensity_stereo_bound;
  }

  final void read_header(BitStream stream) throws IOException {
    int headerstring;
    int channel_bitrate;
    boolean sync = false;
    do {
      headerstring = stream.syncHeader(syncmode);
      if (syncmode == BitStream.INITIAL_SYNC) {
        h_version = ((headerstring >>> 19) & 1);
        if ((h_sample_frequency = ((headerstring >>> 10) & 3)) == 3) {
          return;
        }
      }
      h_layer = 4 - (headerstring >>> 17) & 3;
      // E.B Fix.
      //h_protection_bit = 0;
      h_protection_bit = (headerstring >>> 16) & 1;
      // End.
      h_bitrate_index = (headerstring >>> 12) & 0xF;
      h_padding_bit = (headerstring >>> 9) & 1;
      h_mode = ((headerstring >>> 6) & 3);
      h_mode_extension = (headerstring >>> 4) & 3;
      if (h_mode == JOINT_STEREO) {
        h_intensity_stereo_bound = (h_mode_extension << 2) + 4;
      } else {
        h_intensity_stereo_bound = 0;
      }
      if (h_layer == 1) {
        h_number_of_subbands = 32;
      } else {
        channel_bitrate = h_bitrate_index;
        // calculate bitrate per channel:
        if (h_mode != SINGLE_CHANNEL) {
          if (channel_bitrate == 4) {
            channel_bitrate = 1;
          } else {
            channel_bitrate -= 4;
          }
        }
        if ((channel_bitrate == 1) || (channel_bitrate == 2)) {
          if (h_sample_frequency == THIRTYTWO) {
            h_number_of_subbands = 12;
          } else {
            h_number_of_subbands = 8;
          }
        } else if ((h_sample_frequency == FOURTYEIGHT) || ((channel_bitrate >= 3) && (channel_bitrate <= 5))) {
          h_number_of_subbands = 27;
        } else {
          h_number_of_subbands = 30;
        }
      }
      if (h_intensity_stereo_bound > h_number_of_subbands) {
        h_intensity_stereo_bound = h_number_of_subbands;
      }
      // calculate framesize and nSlots
      calFrameSize();
      // read framedata:
      stream.read_frame_data(framesize);
      if (stream.isSyncCurrentPosition(syncmode)) {
        if (syncmode == BitStream.INITIAL_SYNC) {
          syncmode = BitStream.STRICT_SYNC;
          stream.set_syncword(headerstring & 0xFFF80CC0);
        }
        sync = true;
      }
      else {
        stream.unreadFrame();
      }
    } while (!sync);
    stream.parse_frame();

	// E.B Fix
	if (h_protection_bit == 0)
	{
	   // frame contains a crc checksum
	   short checksum = (short) stream.readbits(16);
	}
	// End
  }

  /* only supports mpeg1 frames; stripped out mpeg2 checking */
  private final void calFrameSize() {
     framesize = (144 * bitrates[h_version] [h_layer - 1] [h_bitrate_index]) / frequencies[h_version] [h_sample_frequency];
     if(h_padding_bit != 0)
       framesize++;

     if(h_version == MPEG1)
       // E.B Fix
       nSlots = framesize - ((h_mode == SINGLE_CHANNEL) ? 17 : 32) -  ((h_protection_bit!=0) ? 0 : 2) - 4;
       //nSlots = framesize - ((h_mode == SINGLE_CHANNEL) ? 17 : 32) - 4;
       // End.

     else{
       System.out.println("sorry,doesn't support mpeg2 frames - only LayerIII is supported");
       System.exit(1);
     }

     framesize -= 4;
  }
}