ADTSDemultiplexer.java

/*
 *  Copyright (C) 2011 in-somnia
 * 
 *  This file is part of JAAD.
 * 
 *  JAAD is free software; you can redistribute it and/or modify it 
 *  under the terms of the GNU Lesser General Public License as 
 *  published by the Free Software Foundation; either version 3 of the 
 *  License, or (at your option) any later version.
 *
 *  JAAD 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 Lesser General 
 *  Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library.
 *  If not, see <http://www.gnu.org/licenses/>.
 */
package net.sourceforge.jaad.adts;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;

public class ADTSDemultiplexer {

	private static final int MAXIMUM_FRAME_SIZE = 6144;
	private PushbackInputStream in;
	private DataInputStream din;
	private boolean first;
	private ADTSFrame frame;

	public ADTSDemultiplexer(InputStream in) throws IOException {
		this.in = new PushbackInputStream(in);
		din = new DataInputStream(this.in);
		first = true;
		if(!findNextFrame()) throw new IOException("no ADTS header found");
	}

	public byte[] getDecoderSpecificInfo() {
		return frame.createDecoderSpecificInfo();
	}

	public byte[] readNextFrame() throws IOException {
		if(first) first = false;
		else findNextFrame();

		byte[] b = new byte[frame.getFrameLength()];
		din.readFully(b);
		return b;
	}

	private boolean findNextFrame() throws IOException {
		//find next ADTS ID
		boolean found = false;
		int left = MAXIMUM_FRAME_SIZE;
		int i;
		while(!found&&left>0) {
			i = in.read();
			left--;
			if(i==0xFF) {
				i = in.read();
				if(((i>>4)&0xF)==0xF) found = true;
				in.unread(i);
			}
		}

		if(found) frame = new ADTSFrame(din);
		return found;
	}

	public int getSampleFrequency() {
		return frame.getSampleFrequency();
	}

	public int getChannelCount() {
		return frame.getChannelCount();
	}
}