bitstream.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.InputStream;
import java.io.IOException;

/**
 *  The <code>Bistream</code> class is responsible for parsing an MPEG audio bitstream. <b>REVIEW:</b> much of the parsing currently occurs in the
 * various decoders. This should be moved into this class and associated inner classes.
 *@author     micah
 *@created    December 8,2001
 */
public final class BitStream {

  static final byte INITIAL_SYNC = 0;
  static final byte STRICT_SYNC = 1;
  private final static int BUFFER_INT_SIZE = 433;
  private final static int bitmask[] = {0,
            0x00000001,0x00000003,0x00000007,0x0000000F,
            0x0000001F,0x0000003F,0x0000007F,0x000000FF,
            0x000001FF,0x000003FF,0x000007FF,0x00000FFF,
            0x00001FFF,0x00003FFF,0x00007FFF,0x0000FFFF,
            0x0001FFFF};

  private static PushBackStream source;
  private static final int[] framebuffer = new int[BUFFER_INT_SIZE];
  private static int framesize;
  private static final byte[] frame_bytes = new byte[BUFFER_INT_SIZE * 4];
  private static int wordpointer;
  private static int bitindex;
  private static int syncword;
  private static boolean single_ch_mode;
  private final static Header header = new Header();
  private final static byte syncbuf[] = new byte[4];


  public BitStream(InputStream in) {
    source = new PushBackStream(in,512);
    closeFrame();
  }

  static int read;

  public final boolean isSyncCurrentPosition(int syncmode) throws IOException {
   if ((read = source.read(syncbuf,0,4)) > 0) {  //if(read>=0){
      source.unread(syncbuf,0,read);
      if (read == 4){
        headerstring = ((syncbuf[0] << 24) & 0xFF000000) | ((syncbuf[1] << 16) & 0x00FF0000) | ((syncbuf[2] << 8) & 0x0000FF00) | ((syncbuf[3] << 0) & 0x000000FF);
        return isSyncMark(headerstring,syncmode,syncword);
      }
    }

    return true;
  }

  /**
   *  Gets the syncMark attribute of the Bitstream object
   *@param  headerstring  Description of Parameter
   *@param  syncmode      Description of Parameter
   *@param  word          Description of Parameter
   *@return               The syncMark value
   */
  static boolean sync;

  public final boolean isSyncMark(int headerstring,int syncmode,int word) {
    if (syncmode == INITIAL_SYNC) {
      sync = ((headerstring & 0xFFF00000) == 0xFFF00000);
    }
    else {
      sync = ((headerstring & 0xFFF80C00) == word) && (((headerstring & 0x000000C0) == 0x000000C0) == single_ch_mode);
    }
    // filter out invalid sample rate
    if(sync)
      if(sync = (((headerstring >>> 10) & 3) != 3))
        if(sync = (((headerstring >>> 17) & 3) != 0))
          sync = (((headerstring >>> 19) & 3) != 1);

    return sync;
  }


  static int sum,returnvalue;

  public final int readbits(int num) {
    sum = bitindex + num;
    if (sum <= 32) {
      returnvalue = (framebuffer[wordpointer] >>> (32 - sum)) & bitmask[num];
      if ((bitindex += num) == 32) {
        bitindex = 0;
        wordpointer++;
      }

      return returnvalue;
    }

    returnvalue = (((framebuffer[wordpointer++] & 0x0000FFFF) << 16) & 0xFFFF0000) | (((framebuffer[wordpointer] & 0xFFFF0000) >>> 16) & 0x0000FFFF);
    returnvalue >>>= 48 - sum;
    returnvalue &= bitmask[num];
    bitindex = sum - 32;
    return returnvalue;
  }

  /**
   *  Description of the Method
   *@exception  IOException  Description of Exception
   */
  public void close() throws IOException {
    source.close();
  }

  /**
   *  Reads and parses the next frame from the input source.
   *@return                  the Header describing details of the frame read,or null if the end of the stream has been reached.
   *@exception  IOException  Description of Exception
   */
  public Header readFrame() throws IOException {
    //if (framesize == -1) {
      header.read_header(this);
    //}
    return header;
  }

  /**
   *  Unreads the bytes read from the frame.
   *@exception  IOException      Description of Exception
   *@throws  BitstreamException
   */
  // REVIEW: add new error codes for this.
  public final void unreadFrame() throws IOException {
    if (wordpointer == -1 && bitindex == -1 && (framesize > 0)) {
      source.unread(frame_bytes,0,framesize);
    }
  }

  /** Description of the Method */
  public void closeFrame() {
    framesize = wordpointer = bitindex = -1;
  }

  /**
   *  Set the word we want to sync the header to. In Big-Endian byte order
   *@param  syncword0  Description of Parameter
   */
  final void set_syncword(int syncword0) {
    syncword = syncword0 & 0xFFFFFF3F;
    single_ch_mode = ((syncword0 & 0x000000C0) == 0x000000C0);
  }

 static int bytesread,headerstring;

   int syncHeader(byte syncmode) throws IOException {
        if((bytesread = source.read(syncbuf,0,3))!= 3)
            return -1;

        headerstring = syncbuf[0] << 16 & 0xff0000 | syncbuf[1] << 8 & 0xff00 | syncbuf[2] << 0 & 0xff;

        do{
            headerstring <<= 8;
            if(source.read(syncbuf,3,1) != 1)
                return -1;
            headerstring |= syncbuf[3] & 0xff;
        }while(!isSyncMark(headerstring,syncmode,syncword));

        return headerstring;
    }

  /**
   *  Reads the data for the next frame. The frame is not parsed until parse frame is called.
   *@param  bytesize         Description of Parameter
   *@exception  IOException  Description of Exception
   */
  final void read_frame_data(int bytesize) throws IOException {
    if(bytesize>=0){
      framesize = bytesize;
      wordpointer = bitindex = -1;
      source.read(frame_bytes,0,bytesize);
    }
  }

  static int b,k;
  static byte b0,b1,b2,b3;

  /** Parses the data previously read with read_frame_data(). */
  final void parse_frame() {
    // Convert Bytes read to int
    for (k = 0,b=0; k < framesize; k += 4) {
      b0 = frame_bytes[k];
      if (k + 3 < framesize) {
        b3 = frame_bytes[k + 3];
        b2 = frame_bytes[k + 2];
        b1 = frame_bytes[k + 1];
      }
      else if (k + 2 < framesize) {
        b3 = 0;
        b2 = frame_bytes[k + 2];
        b1 = frame_bytes[k + 1];
      }
      else if (k + 1 < framesize) {
        b2 = b3 = 0;
        b1 = frame_bytes[k + 1];
      }
      framebuffer[b++] = ((b0 << 24) & 0xFF000000) | ((b1 << 16) & 0x00FF0000) | ((b2 << 8) & 0x0000FF00) | (b3 & 0x000000FF);
    }

    wordpointer = bitindex = 0;
  }

}