|
2
|
1 /* g726_rfc3551.c
|
|
|
2 *
|
|
|
3 * Copyright (C) DFS Deutsche Flugsicherung (2004, 2005).
|
|
|
4 * All Rights Reserved.
|
|
|
5 * Author: Andre Adrian
|
|
|
6 */
|
|
|
7
|
|
|
8
|
|
|
9 /* RFC3551
|
|
|
10
|
|
|
11 name of sampling default
|
|
|
12 encoding sample/frame bits/sample rate ms/frame ms/packet
|
|
|
13 __________________________________________________________________
|
|
|
14 G726-40 sample 5 8,000 20
|
|
|
15 G726-32 sample 4 8,000 20
|
|
|
16 G726-24 sample 3 8,000 20
|
|
|
17 G726-16 sample 2 8,000 20
|
|
|
18
|
|
|
19 Applications MUST
|
|
|
20 determine the encoding type of packed codewords from the RTP payload
|
|
|
21 identifier.
|
|
|
22
|
|
|
23 the first codeword is placed into the first octet
|
|
|
24 such that the least significant bit of the codeword aligns with the
|
|
|
25 least significant bit in the octet, the second codeword is then
|
|
|
26 packed so that its least significant bit coincides with the least
|
|
|
27 significant unoccupied bit in the octet. When a complete codeword
|
|
|
28 cannot be placed into an octet, the bits overlapping the octet
|
|
|
29 boundary are placed into the least significant bits of the next
|
|
|
30 octet. Packing MUST end with a completely packed final octet. The
|
|
|
31 number of codewords packed will therefore be a multiple of 8, 2, 8,
|
|
|
32 and 4 for G726-40, G726-32, G726-24, and G726-16, respectively. An
|
|
|
33 example of the packing scheme for G726-32 codewords is as shown,
|
|
|
34 where bit 7 is the least significant bit of the first octet, and bit
|
|
|
35 A3 is the least significant bit of the first codeword:
|
|
|
36
|
|
|
37 0 1
|
|
|
38 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
|
|
|
39 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|
|
|
40 |B B B B|A A A A|D D D D|C C C C| ...
|
|
|
41 |0 1 2 3|0 1 2 3|0 1 2 3|0 1 2 3|
|
|
|
42 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|
|
|
43
|
|
|
44 An example of the packing scheme for G726-24 codewords follows, where
|
|
|
45 again bit 7 is the least significant bit of the first octet, and bit
|
|
|
46 A2 is the least significant bit of the first codeword:
|
|
|
47
|
|
|
48 0 1 2
|
|
|
49 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
|
|
|
50 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|
|
|
51 |C C|B B B|A A A|F|E E E|D D D|C|H H H|G G G|F F| ...
|
|
|
52 |1 2|0 1 2|0 1 2|2|0 1 2|0 1 2|0|0 1 2|0 1 2|0 1|
|
|
|
53 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|
|
|
54
|
|
|
55 PT encoding media type clock rate channels
|
|
|
56 name (Hz)
|
|
|
57 ___________________________________________________
|
|
|
58 dyn G726-40 A 8,000 1
|
|
|
59 dyn G726-32 A 8,000 1
|
|
|
60 dyn G726-24 A 8,000 1
|
|
|
61 dyn G726-16 A 8,000 1
|
|
|
62
|
|
|
63 */
|
|
|
64
|
|
|
65 #include <string.h>
|
|
|
66 #include "g711.h"
|
|
|
67 #include "g726.h"
|
|
|
68
|
|
|
69 /* G.726 subset: 32kBit/s, A-law */
|
|
|
70
|
|
|
71 static void g726pack(Byte *packed, short *in, int cnt)
|
|
|
72 {
|
|
|
73 int i;
|
|
|
74 for (i = 0; i <= cnt; i += 2, ++packed, ++in) {
|
|
|
75 *packed = (*in & 0xF);
|
|
|
76 ++in;
|
|
|
77 *packed += (*in & 0xF) * 16;
|
|
|
78 }
|
|
|
79 }
|
|
|
80
|
|
|
81 static void g726unpack(short *out, Byte *packed, int cnt)
|
|
|
82 {
|
|
|
83 int i;
|
|
|
84 for (i = 0; i <= cnt; i += 2, ++packed, ++out) {
|
|
|
85 *out = (*packed & 0xF);
|
|
|
86 ++out;
|
|
|
87 *out = (*packed & 0xF0) / 16;
|
|
|
88 }
|
|
|
89 }
|
|
|
90
|
|
|
91 void g726_initEncode(G726_state *encoder_state)
|
|
|
92 {
|
|
|
93 memset(encoder_state, 0, sizeof(G726_state));
|
|
|
94 }
|
|
|
95
|
|
|
96 void g726_initDecode(G726_state *decoder_state)
|
|
|
97 {
|
|
|
98 memset(decoder_state, 0, sizeof(G726_state));
|
|
|
99 }
|
|
|
100
|
|
|
101 short g726_encode( /* (o) Number of bytes encoded */
|
|
|
102 G726_state *state, /* (i/o) Encoder instance */
|
|
|
103 unsigned char *encoded_data, /* (o) The encoded bytes */
|
|
|
104 short *inp_buf /* (i) The signal block to encode */
|
|
|
105 )
|
|
|
106 {
|
|
|
107 unsigned char inpb_buf[20*8];
|
|
|
108 short out_buf[20*8];
|
|
|
109 static char law[] = "1";
|
|
|
110
|
|
|
111 alaw_compress(20*8, inp_buf, inpb_buf);
|
|
|
112 G726_encode(inpb_buf, out_buf, 20*8, law, 4, 0, state);
|
|
|
113 g726pack(encoded_data, out_buf, 20*8);
|
|
|
114
|
|
|
115 return 20*8/2;
|
|
|
116 }
|
|
|
117
|
|
|
118 short g726_decode( /* (o) Number of decoded samples */
|
|
|
119 G726_state *state, /* (i/o) Decoder instance */
|
|
|
120 short *decoded_data, /* (o) Decoded signal block */
|
|
|
121 unsigned char *encoded_data, /* (i) Encoded bytes */
|
|
|
122 short mode /* (i) 0=PL, 1=Normal */
|
|
|
123 )
|
|
|
124 {
|
|
|
125 short inp_buf[20*8];
|
|
|
126 unsigned char outb_buf[20*8];
|
|
|
127 static char law[] = "1";
|
|
|
128
|
|
|
129 g726unpack(inp_buf, encoded_data, 20*8);
|
|
|
130 G726_decode(inp_buf, outb_buf, 20*8, law, 4, 0, state);
|
|
|
131 alaw_expand(20*8, outb_buf, decoded_data);
|
|
|
132
|
|
|
133 return 20*8;
|
|
|
134 }
|
