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/*
Copyright (C) 2016 - 2017, Lefteris Zafiris <zaf@fastmail.com>
This program is free software, distributed under the terms of
the BSD 3-Clause License. See the LICENSE file
at the top of the source tree.
Package g711 implements encoding and decoding of G711 PCM sound data.
G.711 is an ITU-T standard for audio companding.
*/
package g711
const alawClip = 0x7F7B
var (
// A-law quantization segment lookup table
alawSegment = [128]uint8{
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,
}
// A-law to LPCM conversion lookup table
alaw2lpcm = [256]int16{
-5504, -5248, -6016, -5760, -4480, -4224, -4992, -4736,
-7552, -7296, -8064, -7808, -6528, -6272, -7040, -6784,
-2752, -2624, -3008, -2880, -2240, -2112, -2496, -2368,
-3776, -3648, -4032, -3904, -3264, -3136, -3520, -3392,
-22016, -20992, -24064, -23040, -17920, -16896, -19968, -18944,
-30208, -29184, -32256, -31232, -26112, -25088, -28160, -27136,
-11008, -10496, -12032, -11520, -8960, -8448, -9984, -9472,
-15104, -14592, -16128, -15616, -13056, -12544, -14080, -13568,
-344, -328, -376, -360, -280, -264, -312, -296,
-472, -456, -504, -488, -408, -392, -440, -424,
-88, -72, -120, -104, -24, -8, -56, -40,
-216, -200, -248, -232, -152, -136, -184, -168,
-1376, -1312, -1504, -1440, -1120, -1056, -1248, -1184,
-1888, -1824, -2016, -1952, -1632, -1568, -1760, -1696,
-688, -656, -752, -720, -560, -528, -624, -592,
-944, -912, -1008, -976, -816, -784, -880, -848,
5504, 5248, 6016, 5760, 4480, 4224, 4992, 4736,
7552, 7296, 8064, 7808, 6528, 6272, 7040, 6784,
2752, 2624, 3008, 2880, 2240, 2112, 2496, 2368,
3776, 3648, 4032, 3904, 3264, 3136, 3520, 3392,
22016, 20992, 24064, 23040, 17920, 16896, 19968, 18944,
30208, 29184, 32256, 31232, 26112, 25088, 28160, 27136,
11008, 10496, 12032, 11520, 8960, 8448, 9984, 9472,
15104, 14592, 16128, 15616, 13056, 12544, 14080, 13568,
344, 328, 376, 360, 280, 264, 312, 296,
472, 456, 504, 488, 408, 392, 440, 424,
88, 72, 120, 104, 24, 8, 56, 40,
216, 200, 248, 232, 152, 136, 184, 168,
1376, 1312, 1504, 1440, 1120, 1056, 1248, 1184,
1888, 1824, 2016, 1952, 1632, 1568, 1760, 1696,
688, 656, 752, 720, 560, 528, 624, 592,
944, 912, 1008, 976, 816, 784, 880, 848,
}
// A-law to u-law conversion lookup table based on the ITU-T G.711 specification
alaw2ulaw = [256]uint8{
42, 43, 40, 41, 46, 47, 44, 45, 34, 35, 32, 33, 38, 39, 36, 37,
57, 58, 55, 56, 61, 62, 59, 60, 49, 50, 47, 48, 53, 54, 51, 52,
10, 11, 8, 9, 14, 15, 12, 13, 2, 3, 0, 1, 6, 7, 4, 5,
26, 27, 24, 25, 30, 31, 28, 29, 18, 19, 16, 17, 22, 23, 20, 21,
98, 99, 96, 97, 102, 103, 100, 101, 93, 93, 92, 92, 95, 95, 94, 94,
116, 118, 112, 114, 124, 126, 120, 122, 106, 107, 104, 105, 110, 111, 108, 109,
72, 73, 70, 71, 76, 77, 74, 75, 64, 65, 63, 63, 68, 69, 66, 67,
86, 87, 84, 85, 90, 91, 88, 89, 79, 79, 78, 78, 82, 83, 80, 81,
170, 171, 168, 169, 174, 175, 172, 173, 162, 163, 160, 161, 166, 167, 164, 165,
185, 186, 183, 184, 189, 190, 187, 188, 177, 178, 175, 176, 181, 182, 179, 180,
138, 139, 136, 137, 142, 143, 140, 141, 130, 131, 128, 129, 134, 135, 132, 133,
154, 155, 152, 153, 158, 159, 156, 157, 146, 147, 144, 145, 150, 151, 148, 149,
226, 227, 224, 225, 230, 231, 228, 229, 221, 221, 220, 220, 223, 223, 222, 222,
244, 246, 240, 242, 252, 254, 248, 250, 234, 235, 232, 233, 238, 239, 236, 237,
200, 201, 198, 199, 204, 205, 202, 203, 192, 193, 191, 191, 196, 197, 194, 195,
214, 215, 212, 213, 218, 219, 216, 217, 207, 207, 206, 206, 210, 211, 208, 209,
}
)
// EncodeAlaw encodes 16bit LPCM data to G711 A-law PCM
func EncodeAlaw(lpcm []byte) []byte {
if len(lpcm) < 2 {
return []byte{}
}
alaw := make([]byte, len(lpcm)/2)
for i, j := 0, 0; j <= len(lpcm)-2; i, j = i+1, j+2 {
alaw[i] = EncodeAlawFrame(int16(lpcm[j]) | int16(lpcm[j+1])<<8)
}
return alaw
}
// EncodeAlawFrame encodes a 16bit LPCM frame to G711 A-law PCM
func EncodeAlawFrame(frame int16) uint8 {
/*
The algorithm first stores off the sign. Then the code branches.
If the absolute value of the source sample is less than 256, the 16-bit sample is simply
shifted down 4 bits and converted to an 8-bit value, thus losing the top 4 bits in the process.
However, if it is more than 256, a logarithmic algorithm is applied to the sample to
determine the precision to keep. In that case, the sample is shifted down to access the
seven most significant bits of the sample. Those seven bits are then used to determine the
precision of the bottom 4 bits (segment). Finally, the top seven bits are shifted back up four bits
to make room for the bottom 4 bits. The two are then logically OR'd together to create the
eight bit compressed sample. The sign is then applied, and the entire compressed sample
is logically XOR'd for transmission.
*/
sign := ((^frame) >> 8) & 0x80
if sign == 0 {
frame = -frame
}
if frame > alawClip {
frame = alawClip
}
var compressedByte uint8
if frame >= 256 {
segment := alawSegment[(frame>>8)&0x7F]
bottom := (frame >> (segment + 3)) & 0x0F
compressedByte = uint8(((int16(segment) << 4) | bottom))
} else {
compressedByte = uint8(frame >> 4)
}
return compressedByte ^ uint8(sign^0x55)
}
// DecodeAlaw decodes A-law PCM data to 16bit LPCM
func DecodeAlaw(pcm []byte) []byte {
lpcm := make([]byte, len(pcm)*2)
for i, j := 0, 0; i < len(pcm); i, j = i+1, j+2 {
frame := alaw2lpcm[pcm[i]]
lpcm[j] = byte(frame)
lpcm[j+1] = byte(frame >> 8)
}
return lpcm
}
// DecodeAlawFrame decodes an A-law PCM frame to 16bit LPCM
func DecodeAlawFrame(frame uint8) int16 {
return alaw2lpcm[frame]
}
// Alaw2Ulaw performs direct A-law to u-law data conversion
func Alaw2Ulaw(alaw []byte) []byte {
ulaw := make([]byte, len(alaw))
for i := 0; i < len(alaw); i++ {
ulaw[i] = alaw2ulaw[alaw[i]]
}
return ulaw
}
// Alaw2UlawFrame directly converts an A-law frame to u-law
func Alaw2UlawFrame(frame uint8) uint8 {
return alaw2ulaw[frame]
}
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