SampleScaleBox.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.mp4.boxes.impl;

import java.io.IOException;
import net.sourceforge.jaad.mp4.MP4InputStream;
import net.sourceforge.jaad.mp4.boxes.FullBox;

/**
 * This box may be present in any visual sample entry. This box indicates the
 * scaling method that is applied when the width and height of the visual
 * material (as declared by the width and height values in any visual sample
 * entry) do not match the track width and height values (as indicated in the
 * track header box).
 * Implementation of this box is optional; if this box is present and can be
 * interpreted by the decoder, all samples shall be displayed according to the
 * scaling behaviour that is specified in this box. Otherwise, all samples are
 * scaled to the size that is indicated by the width and height field in the
 * Track Header Box.
 * If the size of the image is bigger than the size of the presentation region
 * and 'hidden' scaling is applied in the Sample Scale Box, it is not possible
 * to display the whole image. In such a case, it is useful to provide the
 * information to determine the region that is to be displayed. The centre
 * values would then indicate the centre of the region of high priority in each
 * visual sample. The decoder can display the region of high priority according
 * to these values. The centre values imply a consistent crop for all the images
 * in a sequence. The offset values are positive when the desired visual centre
 * is below or to the right of the image centre, and negative for offsets above
 * or to the left.
 * 
 * @author in-somnia
 */
public class SampleScaleBox extends FullBox {

	private boolean constrained;
	private int scaleMethod, displayCenterX, displayCenterY;

	public SampleScaleBox() {
		super("Sample Scale Box");
	}

	@Override
	public void decode(MP4InputStream in) throws IOException {
		super.decode(in);

		//7 bits reserved, 1 bit flag
		constrained = (in.read()&1)==1;

		scaleMethod = in.read();
		displayCenterX = (int) in.readBytes(2);
		displayCenterY = (int) in.readBytes(2);
	}

	/**
	 * If this flag is set, all samples described by this sample entry shall be 
	 * scaled according to the method specified by the field 'scale_method'.
	 * Otherwise, it is recommended that all the samples be scaled according to
	 * the method specified by the field 'scale_method', but can be displayed in
	 * an implementation dependent way, which may include not scaling the image
	 * (i.e. neither to the width and height specified in the track header box,
	 * nor by the method indicated here).
	 *
	 * @return true if the samples should be scaled by the scale method
	 */
	public boolean isConstrained() {
		return constrained;
	}

	/**
	 * The horizontal offset in pixels of the centre of the region that should
	 * be displayed by priority relative to the centre of the image. Default
	 * value is zero. Positive values indicate a display centre to the right of
	 * the image centre.
	 *
	 * @return the horizontal offset
	 */
	public int getDisplayCenterX() {
		return displayCenterX;
	}

	/**
	 * The vertical offset in pixels of the centre of the region that should be 
	 * displayed by priority relative to the centre of the image. Default value
	 * is zero. Positive values indicate a display centre below the image
	 * centre.
	 * @return the vertical offset
	 */
	public int getDisplayCenterY() {
		return displayCenterY;
	}

	/**
	 * The scale method is an integer that defines the scaling mode to be used.
	 * Of the 256 possible values the values 0 through 127 are reserved for use
	 * by ISO and values 128 through 255 are user-defined and are not specified
	 * in this International Standard; they may be used as determined by the
	 * application. Of the reserved values the following modes are currently
	 * defined:
	 * 1: scaling is done by 'fill' mode.
	 * 2: scaling is done by 'hidden' mode.
	 * 3: scaling is done by 'meet' mode.
	 * 4: scaling is done by 'slice' mode in the x-coordinate.
	 * 5: scaling is done by 'slice' mode in the y-coordinate.
	 *
	 * @return the scale method
	 */
	public int getScaleMethod() {
		return scaleMethod;
	}
}