68 lines
1.9 KiB
C#
68 lines
1.9 KiB
C#
|
using System;
|
|||
|
|
using System.Collections.Generic;
|
|||
|
|
using System.Linq;
|
|||
|
|
using System.Text;
|
|||
|
|
using System.Threading.Tasks;
|
|||
|
|
|
|||
|
|
namespace SipComponent.NAudio.Codecs
|
|||
|
|
{
|
|||
|
|
/// <summary>
|
|||
|
|
/// A-law encoder
|
|||
|
|
/// </summary>
|
|||
|
|
public static class ALawEncoder
|
|||
|
|
{
|
|||
|
|
private const int cBias = 0x84;
|
|||
|
|
private const int cClip = 32635;
|
|||
|
|
private static readonly byte[] ALawCompressTable = new byte[128]
|
|||
|
|
{
|
|||
|
|
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
|
|||
|
|
};
|
|||
|
|
|
|||
|
|
/// <summary>
|
|||
|
|
/// Encodes a single 16 bit sample to a-law
|
|||
|
|
/// </summary>
|
|||
|
|
/// <param name="sample">16 bit PCM sample</param>
|
|||
|
|
/// <returns>a-law encoded byte</returns>
|
|||
|
|
public static byte LinearToALawSample(short sample)
|
|||
|
|
{
|
|||
|
|
int sign;
|
|||
|
|
int exponent;
|
|||
|
|
int mantissa;
|
|||
|
|
byte compressedByte;
|
|||
|
|
|
|||
|
|
sign = ((~sample) >> 8) & 0x80;
|
|||
|
|
if (sign == 0)
|
|||
|
|
sample = (short)-sample;
|
|||
|
|
if (sample > cClip)
|
|||
|
|
sample = cClip;
|
|||
|
|
if (sample >= 256)
|
|||
|
|
{
|
|||
|
|
exponent = (int)ALawCompressTable[(sample >> 8) & 0x7F];
|
|||
|
|
mantissa = (sample >> (exponent + 3)) & 0x0F;
|
|||
|
|
compressedByte = (byte)((exponent << 4) | mantissa);
|
|||
|
|
}
|
|||
|
|
else
|
|||
|
|
{
|
|||
|
|
compressedByte = (byte)(sample >> 4);
|
|||
|
|
}
|
|||
|
|
compressedByte ^= (byte)(sign ^ 0x55);
|
|||
|
|
return compressedByte;
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}
|