media/java/android/media/videoeditor/WaveformData.java

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


package android.media.videoeditor;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * Class which describes the waveform data of an audio track. The gain values
 * represent the average gain for an audio frame. For audio codecs which do not
 * operate on a per frame bases (eg. ALAW, ULAW) a reasonable audio frame
 * duration will be assumed (eg. 50ms).
 * {@hide}
 */
public class WaveformData {
    /*
     *  Instance variables
     */
    private final int mFrameDurationMs;
    private final int mFramesCount;
    private final short[] mGains;

    /*
     * This constructor shall not be used
     */
    @SuppressWarnings("unused")
    private WaveformData() throws IOException {
        mFrameDurationMs = 0;
        mFramesCount = 0;
        mGains = null;
    }

    /*
     * Constructor
     *
     * @param audioWaveformFilename The name of the audio waveform file
     *
     * The file format is as following:
     * <ul>
     *  <li>first 4 bytes provide the number of samples for each value, as
     *  big-endian signed</li>
     *  <li>4 following bytes is the total number of values in the file, as
     *  big-endian signed</li>
     *  <li>then, all values follow as bytes</li>
     * </ul>
     *
     * @throws IOException on failure of file input stream operations
     * @throws IllegalArgumentException if audioWaveformFilename is null
     */
    WaveformData(String audioWaveformFilename) throws IOException {

        if (audioWaveformFilename == null) {
            throw new IllegalArgumentException("WaveformData : filename is null");
        }

        FileInputStream audioGraphFileReadHandle = null;

        try {
            final File audioGraphFileContext = new File(audioWaveformFilename);

            audioGraphFileReadHandle = new FileInputStream(audioGraphFileContext);
            /*
             * Read frame duration
             */
            final byte tempFrameDuration[] = new byte[4];

            audioGraphFileReadHandle.read(tempFrameDuration, 0, 4);

            int tempFrameDurationMs = 0;
            int tempFramesCounter = 0;
            for (int i = 0; i < 4; i++) {
                tempFrameDurationMs = (tempFrameDurationMs << 8);
                tempFrameDurationMs = (tempFrameDurationMs | (tempFrameDuration[i] & 0xff));
            }
            mFrameDurationMs = tempFrameDurationMs;

            /*
             * Read count
             */
            final byte tempFramesCount[] = new byte[4];

            audioGraphFileReadHandle.read(tempFramesCount, 0, 4);
            for (int i = 0; i < 4; i++) {
                tempFramesCounter = (tempFramesCounter << 8);
                tempFramesCounter = (tempFramesCounter | (tempFramesCount[i] & 0xff));
            }
            mFramesCount = tempFramesCounter;

            /*
             *  Capture the graph values
             */
            mGains = new short[mFramesCount];

            for (int i = 0; i < mFramesCount; i++) {
                mGains[i] = (short)audioGraphFileReadHandle.read();
            }
        } finally {
            if (audioGraphFileReadHandle != null) {
                audioGraphFileReadHandle.close();
            }
        }
    }

    /**
     * @return The duration of a frame in milliseconds
     */
    public int getFrameDuration() {
        return mFrameDurationMs;
    }

    /**
     * @return The number of frames within the waveform data
     */
    public int getFramesCount() {
        return mFramesCount;
    }

    /**
     * @return The array of frame gains. The size of the array is the frames
     *         count. The values of the frame gains range from 0 to 255.
     */
    public short[] getFrameGains() {
        return mGains;
    }
}