ResampleInputStream.java revision b798689749c64baba81f02e10cf2157c747d6b46 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.media;
18
19import android.util.Config;
20import android.util.Log;
21
22import java.io.InputStream;
23import java.io.IOException;
24
25
26/**
27 * ResampleInputStream
28 * @hide
29 */
30public final class ResampleInputStream extends InputStream
31{
32    static {
33        System.loadLibrary("media_jni");
34    }
35
36    private final static String TAG = "ResampleInputStream";
37
38    // pcm input stream
39    private InputStream mInputStream;
40
41    // sample rates, assumed to be normalized
42    private final int mRateIn;
43    private final int mRateOut;
44
45    // input pcm data
46    private byte[] mBuf;
47    private int mBufCount;
48
49    // length of 2:1 fir
50    private static final int mFirLength = 29;
51
52    // helper for bytewise read()
53    private final byte[] mOneByte = new byte[1];
54
55    /**
56     * Create a new ResampleInputStream, which converts the sample rate
57     * @param inputStream InputStream containing 16 bit PCM.
58     * @param rateIn the input sample rate.
59     * @param rateOut the output sample rate.
60     * This only handles rateIn == rateOut / 2 for the moment.
61     */
62    public ResampleInputStream(InputStream inputStream, int rateIn, int rateOut) {
63        // only support 2:1 at the moment
64        if (rateIn != 2 * rateOut) throw new IllegalArgumentException("only support 2:1 at the moment");
65        rateIn = 2;
66        rateOut = 1;
67
68        mInputStream = inputStream;
69        mRateIn = rateIn;
70        mRateOut = rateOut;
71    }
72
73    @Override
74    public int read() throws IOException {
75        int rtn = read(mOneByte, 0, 1);
76        return rtn == 1 ? (0xff & mOneByte[0]) : -1;
77    }
78
79    @Override
80    public int read(byte[] b) throws IOException {
81        return read(b, 0, b.length);
82    }
83
84    @Override
85    public int read(byte[] b, int offset, int length) throws IOException {
86        if (mInputStream == null) throw new IllegalStateException("not open");
87
88        // ensure that mBuf is big enough to cover requested 'length'
89        int nIn = ((length / 2) * mRateIn / mRateOut + mFirLength) * 2;
90        if (mBuf == null) {
91            mBuf = new byte[nIn];
92        } else if (nIn > mBuf.length) {
93            byte[] bf = new byte[nIn];
94            System.arraycopy(mBuf, 0, bf, 0, mBufCount);
95            mBuf = bf;
96        }
97
98        // read until we have enough data for at least one output sample
99        while (true) {
100            int len = ((mBufCount / 2 - mFirLength) * mRateOut / mRateIn) * 2;
101            if (len > 0) {
102                length = len < length ? len : (length / 2) * 2;
103                break;
104            }
105            // TODO: should mBuf.length below be nIn instead?
106            int n = mInputStream.read(mBuf, mBufCount, mBuf.length - mBufCount);
107            if (n == -1) return -1;
108            mBufCount += n;
109        }
110
111        // resample input data
112        fir21(mBuf, 0, b, offset, length / 2);
113
114        // move any unused bytes to front of mBuf
115        int nFwd = length * mRateIn / mRateOut;
116        mBufCount -= nFwd;
117        if (mBufCount > 0) System.arraycopy(mBuf, nFwd, mBuf, 0, mBufCount);
118
119        return length;
120    }
121
122/*
123    @Override
124    public int available() throws IOException {
125        int nsamples = (mIn - mOut + mInputStream.available()) / 2;
126        return ((nsamples - mFirLength) * mRateOut / mRateIn) * 2;
127    }
128*/
129
130    @Override
131    public void close() throws IOException {
132        try {
133            if (mInputStream != null) mInputStream.close();
134        } finally {
135            mInputStream = null;
136        }
137    }
138
139    @Override
140    protected void finalize() throws Throwable {
141        if (mInputStream != null) {
142            close();
143            throw new IllegalStateException("someone forgot to close ResampleInputStream");
144        }
145    }
146
147    //
148    // fir filter code JNI interface
149    //
150    private static native void fir21(byte[] in, int inOffset,
151            byte[] out, int outOffset, int npoints);
152
153}
154