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A generic parser and writer for all ISO 14496 based files (MP4, Quicktime, DCF, PDCF, ...)
There is a newer version: 1.1.22
/*
Copyright (c) 2011 Stanislav Vitvitskiy

Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify,
merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be included in all copies or
substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
OR OTHER DEALINGS IN THE SOFTWARE.
*/
package com.googlecode.mp4parser.h264.read;

import com.googlecode.mp4parser.h264.CharCache;

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

/**
 * A dummy implementation of H264 RBSP reading
 *
 * @author Stanislav Vitvitskiy
 */
public class BitstreamReader {
    private InputStream is;
    private int curByte;
    private int nextByte;
    int nBit;
    protected static int bitsRead;

    protected CharCache debugBits = new CharCache(50);

    public BitstreamReader(InputStream is) throws IOException {
        this.is = is;
        curByte = is.read();
        nextByte = is.read();
    }

    public boolean readBool() throws IOException {
        return read1Bit() == 1;
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#read1Bit()
      */
    public int read1Bit() throws IOException {
        if (nBit == 8) {
            advance();
            if (curByte == -1) {
                return -1;
            }
        }
        int res = (curByte >> (7 - nBit)) & 1;
        nBit++;

        debugBits.append(res == 0 ? '0' : '1');
        ++bitsRead;

        return res;
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#readNBit(int)
      */
    public long readNBit(int n) throws IOException {
        if (n > 64)
            throw new IllegalArgumentException("Can not readByte more then 64 bit");

        long val = 0;

        for (int i = 0; i < n; i++) {
            val <<= 1;
            val |= read1Bit();
        }

        return val;
    }

    private void advance() throws IOException {
        curByte = nextByte;
        nextByte = is.read();
        nBit = 0;
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#readByte()
      */
    public int readByte() throws IOException {
        if (nBit > 0) {
            advance();
        }

        int res = curByte;

        advance();

        return res;
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#moreRBSPData()
      */
    public boolean moreRBSPData() throws IOException {
        if (nBit == 8) {
            advance();
        }
        int tail = 1 << (8 - nBit - 1);
        int mask = ((tail << 1) - 1);
        boolean hasTail = (curByte & mask) == tail;

        return !(curByte == -1 || (nextByte == -1 && hasTail));
    }

    public long getBitPosition() {
        return (bitsRead * 8 + (nBit % 8));
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#readRemainingByte()
      */
    public long readRemainingByte() throws IOException {
        return readNBit(8 - nBit);
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#next_bits(int)
      */
    public int peakNextBits(int n) throws IOException {
        if (n > 8)
            throw new IllegalArgumentException("N should be less then 8");
        if (nBit == 8) {
            advance();
            if (curByte == -1) {
                return -1;
            }
        }
        int[] bits = new int[16 - nBit];

        int cnt = 0;
        for (int i = nBit; i < 8; i++) {
            bits[cnt++] = (curByte >> (7 - i)) & 0x1;
        }

        for (int i = 0; i < 8; i++) {
            bits[cnt++] = (nextByte >> (7 - i)) & 0x1;
        }

        int result = 0;
        for (int i = 0; i < n; i++) {
            result <<= 1;
            result |= bits[i];
        }

        return result;
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#byte_aligned()
      */
    public boolean isByteAligned() {
        return (nBit % 8) == 0;
    }

    /*
      * (non-Javadoc)
      *
      * @see ua.org.jplayer.javcodec.h264.RBSPInputStream#close()
      */
    public void close() throws IOException {
    }

    public int getCurBit() {
        return nBit;
    }
}