G711Codec.java
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package cn.org.hentai.jtt1078.codec;
import cn.org.hentai.jtt1078.codec.AudioCodec;
/**
* 核心转换，PCM转G711
* Created by onlygx
*/
public class G711Codec extends AudioCodec
{
private final static int SIGN_BIT = 0x80;
private final static int QUANT_MASK = 0xf;
private final static int SEG_SHIFT = 4;
private final static int SEG_MASK = 0x70;
static short[] seg_end = {0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF};
private final static int cClip = 32635;
private static final byte[] aLawCompressTable = new byte[]{1, 1, 2, 2, 3, 3, 3,
3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7};
private static byte linearToALawSample(short sample) {
int sign;
int exponent;
int mantissa;
int s;
sign = ((~sample) >> 8) & 0x80;
if (!(sign == 0x80)) {
sample = (short) -sample;
}
if (sample > cClip) {
sample = cClip;
}
if (sample >= 256) {
exponent = aLawCompressTable[(sample >> 8) & 0x7F];
mantissa = (sample >> (exponent + 3)) & 0x0F;
s = (exponent << 4) | mantissa;
} else {
s = sample >> 4;
}
s ^= (sign ^ 0x55);
return (byte) s;
}
/**
* PCM转G711
*
* @param src 编码前的数据
* @return 编码后res数组长度应为编码前src数组长度的一半
*/
public static byte[] encode(byte[] src) {
int j = 0;
int len = src.length;
int count = len / 2;
byte[] res = new byte[count];
short sample = 0;
for (int i = 0; i < count; i++) {
sample = (short) (((src[j++] & 0xff) | (src[j++]) << 8));
res[i] = linearToALawSample(sample);
}
return res;
}
static short search(short val, short[] table, short size) {
for (short i = 0; i < size; i++) {
if (val <= table[i]) {
return i;
}
}
return size;
}
public static byte linear2alaw(short pcm_val) {
short mask;
short seg;
char aval;
if (pcm_val >= 0) {
mask = 0xD5;
} else {
mask = 0x55;
pcm_val = (short) (-pcm_val - 1);
}
/* Convert the scaled magnitude to segment number. */
seg = search(pcm_val, seg_end, (short) 8);
/* Combine the sign, segment, and quantization bits. */
if (seg >= 8) /* out of range, return maximum value. */ return (byte) (0x7F ^ mask);
else {
aval = (char) (seg << SEG_SHIFT);
if (seg < 2) aval |= (pcm_val >> 4) & QUANT_MASK;
else aval |= (pcm_val >> (seg + 3)) & QUANT_MASK;
return (byte) (aval ^ mask);
}
}
public static short alaw2linear(byte a_val) {
short t;
short seg;
a_val ^= 0x55;
t = (short) ((a_val & QUANT_MASK) << 4);
seg = (short) ((a_val & SEG_MASK) >> SEG_SHIFT);
switch (seg) {
case 0:
t += 8;
break;
case 1:
t += 0x108;
break;
default:
t += 0x108;
t <<= seg - 1;
}
return (a_val & SIGN_BIT) != 0 ? t : (short) -t;
}
// 由G.711转至PCM
public static byte[] _toPCM(byte[] g711data) {
byte[] pcmdata = new byte[g711data.length * 2];
for (int i = 0, k = 0; i < g711data.length; i++) {
short v = alaw2linear(g711data[i]);
pcmdata[k++] = (byte) (v & 0xff);
pcmdata[k++] = (byte) ((v >> 8) & 0xff);
}
return pcmdata;
}
// 由PCM转至G.711
public static byte[] _fromPCM(byte[] pcmData) {
return encode(pcmData);
}
@Override
public byte[] toPCM(byte[] data) {
byte[] temp;
// 如果前四字节是00 01 52 00，则是海思头，需要去掉
if (data[0] == 0x00 && data[1] == 0x01 && (data[2] & 0xff) == (data.length - 4) / 2 && data[3] == 0x00) {
temp = new byte[data.length - 4];
System.arraycopy(data, 4, temp, 0, temp.length);
} else temp = data;
return _toPCM(temp);
}
@Override
public byte[] fromPCM(byte[] data) {
return encode(data);
}
}