PCM与G711A互转
工具类（Java）
public class G711Code {
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};
static short search(short val,short[] table,short size){
for (short i = 0 ; i < size; i++) {
if(val <= table[i]){
return i;
}
}
return size;
}
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);
if(pcm_val < 0){
pcm_val = 32767;
}
}
/* 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);
}
}
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;
}
/**
* pcm 转 g711a
* @param pcm
* @param code
* @param size
*/
public static void G711aEncoder(short[] pcm,byte[] code,int size){
for(int i=0;i<size;i++){
code[i]=linear2alaw(pcm[i]);
// Log.e("-------------","数据编码:"+code[i]);
}
}
/**
* g711a 转 pcm
* @param pcm
* @param code
* @param size
*/
public static void G711aDecoder(short[] pcm,byte[] code,int size){
for(int i=0;i<size;i++){
pcm[i]=alaw2linear(code[i]);
}
}
/**
* byte转short
* @param data
* @return
*/
public static short[] byteToShort(byte[] data) {
short[] shortValue = new short[data.length / 2];
for (int i = 0; i < shortValue.length; i++) {
shortValue[i] = (short) ((data[i * 2] & 0xff) | ((data[i * 2 + 1] & 0xff) << 8));
}
return shortValue;
}
/**
* short转byte
* @param data
* @return
*/
public static byte[] shortToByte(short[] data) {
byte[] byteValue = new byte[data.length * 2];
for (int i = 0; i < data.length; i++) {
byteValue[i * 2] = (byte) (data[i] & 0xff);
byteValue[i * 2 + 1] = (byte) ((data[i] & 0xff00) >> 8);
}
return byteValue;
}
}
调用方法（Kotlin）
/**
* ffmpeg -f s16le -i customAudio1.pcm -f alaw customAudio1.pcm.g711a
* ffplay -f s16le -ar 8000 customAudio1.pcm
* ffplay -f alaw -ar 8000 customAudio1.pcm.g711a
*
* 可以用进制软件比如hexviewer查看对比ffmpeg转化的g711a文件
* 或者使用ffplay播放显示波形
*/
fun pcm2g711a(){
val inputStream: InputStream = assets.open("customAudio1.pcm")
val available = inputStream.available()
Log.e("TAG","available:"+available)
val bytes: ByteArray = ByteArray(available)
val byteCount = inputStream.read(bytes)
Log.e("TAG","byteCount:"+byteCount)
//文件大可能需要循环读取
// val bytes: ByteArray = ByteArray(1024)
// var byteCount = inputStream.read(bytes)
// Log.e("TAG","start byteCount:"+byteCount)
// while (byteCount != -1){
// byteCount = inputStream.read(bytes)
// Log.e("TAG","byteCount:"+byteCount)
// }
// Log.e("TAG","end byteCount:"+byteCount)
val shortPCM: ShortArray = G711Code.byteToShort(bytes)//一定要转！！！
val bytesG711A: ByteArray = ByteArray(available)
Log.e("TAG","shortPCM.size:"+shortPCM.size)
G711Code.G711aEncoder(shortPCM,bytesG711A,shortPCM.size)
Log.e("TAG","bytesG711A.size:"+bytesG711A.size)
val file = File(getExternalFilesDir(null)?.absolutePath+"/customAudio1_"+System.currentTimeMillis()+".g711a")
val fos = FileOutputStream(file)
fos.write(bytesG711A)
Log.e("TAG","write end")
inputStream.close()
fos.flush()
fos.close()
}
fun g711a2pcm(){
val inputStream: InputStream = assets.open("customAudio1.pcm.g711a")
val available = inputStream.available()
Log.e("TAG","available:"+available)
val bytes: ByteArray = ByteArray(available)
val byteCount = inputStream.read(bytes)
Log.e("TAG","byteCount:"+byteCount)
//文件大可能需要循环读取
// val bytes: ByteArray = ByteArray(1024)
// var byteCount = inputStream.read(bytes)
// Log.e("TAG","start byteCount:"+byteCount)
// while (byteCount != -1){
// byteCount = inputStream.read(bytes)
// Log.e("TAG","byteCount:"+byteCount)
// }
// Log.e("TAG","end byteCount:"+byteCount)
// val bytesPCMEmpty: ByteArray = ByteArray(available)
// Log.e("TAG","bytesPCMEmpty.size:"+bytesPCMEmpty.size)
// val shortPCM: ShortArray = G711Code.byteToShort(bytesPCMEmpty)//会丢失后面一段数据！！！
val shortPCM: ShortArray = ShortArray(available)
Log.e("TAG","shortPCM.size:"+shortPCM.size)
G711Code.G711aDecoder(shortPCM,bytes,bytes.size)
Log.e("TAG","shortPCM.size:"+shortPCM.size)
val file = File(getExternalFilesDir(null)?.absolutePath+"/customAudio1_"+System.currentTimeMillis()+".pcm")
val fos = FileOutputStream(file)
val bytesPCM: ByteArray = G711Code.shortToByte(shortPCM)
fos.write(bytesPCM)
Log.e("TAG","write end")
inputStream.close()
fos.flush()
fos.close()
}