PelAspectRatio.java

/***************************************
 *            ViPER-MPEG               *
 *  The Video Processing               *
 *         Evaluation Resource         *
 *             MPEG-1 Decoder          *
 * Distributed under the LGPL license  *
 *        Terms available at gnu.org.  *
 *                                     *
 *  Copyright University of Maryland,  *
 *                      College Park.  *
 ***************************************/
package edu.umd.cfar.lamp.mpeg1.video;

import java.io.*;

import edu.columbia.ee.flavor.*;
import edu.umd.cfar.lamp.mpeg1.*;
import edu.umd.cfar.lamp.viper.geometry.*;

/**
 * Parses and interprets the pixel aspect ratio of an MPEG-1 file. For more
 * information, see the MPEG-1 spec or http://www.mir.com/DMG/aspect.html .
 */
public class PelAspectRatio implements Parsable {
	private int value = 0;

	public static final Rational[] RATIONAL_PEL_RATIOS = { null,
			new Rational(1), new Rational(6735, 10000),
			new Rational(7031, 10000), new Rational(7615, 10000),
			new Rational(8055, 10000), new Rational(8437, 10000),
			new Rational(8935, 10000), new Rational(54, 59),
			new Rational(9815, 10000), new Rational(10255, 10000),
			new Rational(10695, 10000), new Rational(11, 10),
			new Rational(11575, 10000), new Rational(12015, 10000) };
	public static final float[] PEL_RATIOS = { Float.NaN, 1f, 0.6735f, 0.7031f,
			0.7615f, 0.8055f, 0.8437f, 0.8935f, 0.9157f, 0.9815f, 1.0255f,
			1.0695f, 1.095f, 1.1575f, 1.2015f };

	public PelAspectRatio() {
	}

	/**
	 * @param i
	 */
	public PelAspectRatio(int i) {
		try {
			setValue(i);
		} catch (ParsingException e) {
			throw new IllegalArgumentException(
					"Not a valid aspect ratio index: " + i);
		}
	}

	public void parse(Bitstream bitstream) throws IOException {
		if (value > 0) {
			throw new IllegalStateException("Already parsed!");
		}
		int s = bitstream.nextbits(4);
		setValue(s);
		bitstream.skipbits(4);
	}

	/**
	 * @param newValue
	 * @throws ParsingException
	 */
	private void setValue(int newValue) throws ParsingException {
		if (newValue < PEL_RATIOS.length) {
			if (newValue == 0) {
				throw new ParsingException(
						"Value 0 for PelAspectRatio forbidden.");
			} else {
				value = newValue;
			}
		} else {
			throw new ParsingException("Value " + newValue
					+ " for PelAspectRatio reserved.");
		}
	}

	public float getFloatValue() {
		return PEL_RATIOS[value];
	}

	public Rational getRationalValue() {
		return RATIONAL_PEL_RATIOS[value];
	}

	/**
	 * Gets the index of the pel aspect ratio.
	 * @return Returns the ratio index.
	 */
	public int getValue() {
		return value;
	}
}