ResampleInputStream.java

/*
 * Copyright (C) 2008 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;

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


/**
 * ResampleInputStream
 * @hide
 */
public final class ResampleInputStream extends InputStream
{    
    static {
        System.loadLibrary("media_jni");
    }
    
    private final static String TAG = "ResampleInputStream";
    
    // pcm input stream
    private InputStream mInputStream;

    // sample rates, assumed to be normalized
    private final int mRateIn;
    private final int mRateOut;
    
    // input pcm data
    private byte[] mBuf;
    private int mBufCount;
    
    // length of 2:1 fir
    private static final int mFirLength = 29;
    
    // helper for bytewise read()
    private final byte[] mOneByte = new byte[1];
    
    /**
     * Create a new ResampleInputStream, which converts the sample rate
     * @param inputStream InputStream containing 16 bit PCM.
     * @param rateIn the input sample rate.
     * @param rateOut the output sample rate.
     * This only handles rateIn == rateOut / 2 for the moment.
     */
    public ResampleInputStream(InputStream inputStream, int rateIn, int rateOut) {
        // only support 2:1 at the moment
        if (rateIn != 2 * rateOut) throw new IllegalArgumentException("only support 2:1 at the moment");
        rateIn = 2;
        rateOut = 1;

        mInputStream = inputStream;
        mRateIn = rateIn;
        mRateOut = rateOut;
    }

    @Override
    public int read() throws IOException {
        int rtn = read(mOneByte, 0, 1);
        return rtn == 1 ? (0xff & mOneByte[0]) : -1;
    }
    
    @Override
    public int read(byte[] b) throws IOException {
        return read(b, 0, b.length);
    }

    @Override
    public int read(byte[] b, int offset, int length) throws IOException {
        if (mInputStream == null) throw new IllegalStateException("not open");

        // ensure that mBuf is big enough to cover requested 'length'
        int nIn = ((length / 2) * mRateIn / mRateOut + mFirLength) * 2;
        if (mBuf == null) {
            mBuf = new byte[nIn];
        } else if (nIn > mBuf.length) {
            byte[] bf = new byte[nIn];
            System.arraycopy(mBuf, 0, bf, 0, mBufCount);
            mBuf = bf;
        }
        
        // read until we have enough data for at least one output sample
        while (true) {
            int len = ((mBufCount / 2 - mFirLength) * mRateOut / mRateIn) * 2;
            if (len > 0) {
                length = len < length ? len : (length / 2) * 2;
                break;
            }
            // TODO: should mBuf.length below be nIn instead?
            int n = mInputStream.read(mBuf, mBufCount, mBuf.length - mBufCount);
            if (n == -1) return -1;
            mBufCount += n;
        }

        // resample input data
        fir21(mBuf, 0, b, offset, length / 2);
        
        // move any unused bytes to front of mBuf
        int nFwd = length * mRateIn / mRateOut;
        mBufCount -= nFwd;
        if (mBufCount > 0) System.arraycopy(mBuf, nFwd, mBuf, 0, mBufCount);
        
        return length;
    }

/*
    @Override
    public int available() throws IOException {
        int nsamples = (mIn - mOut + mInputStream.available()) / 2;
        return ((nsamples - mFirLength) * mRateOut / mRateIn) * 2;
    }
*/

    @Override
    public void close() throws IOException {
        try {
            if (mInputStream != null) mInputStream.close();
        } finally {
            mInputStream = null;
        }
    }

    @Override
    protected void finalize() throws Throwable {
        if (mInputStream != null) {
            close();
            throw new IllegalStateException("someone forgot to close ResampleInputStream");
        }
    }

    //
    // fir filter code JNI interface
    //
    private static native void fir21(byte[] in, int inOffset,
            byte[] out, int outOffset, int npoints);

}