Improving rate control for low bitrate
[opus.git] / silk / control_SNR.c
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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "main.h"
33 #include "tuning_parameters.h"
34
35 /* These tables hold SNR values divided by 21 (so they fit in 8 bits)
36    for different target bitrates spaced at 400 bps interval. The first
37    10 values are omitted (0-4 kb/s) because they're all zeros.
38    These tables were obtained by running different SNRs through the
39    encoder and measuring the active bitrate. */
40 static const unsigned char silk_TargetRate_NB_21[117 - 10] = {
41                                               0, 15, 39, 52, 61, 68,
42      74, 79, 84, 88, 92, 95, 99,102,105,108,111,114,117,119,122,124,
43     126,129,131,133,135,137,139,142,143,145,147,149,151,153,155,157,
44     158,160,162,163,165,167,168,170,171,173,174,176,177,179,180,182,
45     183,185,186,187,189,190,192,193,194,196,197,199,200,201,203,204,
46     205,207,208,209,211,212,213,215,216,217,219,220,221,223,224,225,
47     227,228,230,231,232,234,235,236,238,239,241,242,243,245,246,248,
48     249,250,252,253,255
49 };
50
51 static const unsigned char silk_TargetRate_MB_21[165 - 10] = {
52                                               0,  0, 28, 43, 52, 59,
53      65, 70, 74, 78, 81, 85, 87, 90, 93, 95, 98,100,102,105,107,109,
54     111,113,115,116,118,120,122,123,125,127,128,130,131,133,134,136,
55     137,138,140,141,143,144,145,147,148,149,151,152,153,154,156,157,
56     158,159,160,162,163,164,165,166,167,168,169,171,172,173,174,175,
57     176,177,178,179,180,181,182,183,184,185,186,187,188,188,189,190,
58     191,192,193,194,195,196,197,198,199,200,201,202,203,203,204,205,
59     206,207,208,209,210,211,212,213,214,214,215,216,217,218,219,220,
60     221,222,223,224,224,225,226,227,228,229,230,231,232,233,234,235,
61     236,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,
62     251,252,253,254,255
63 };
64
65 static const unsigned char silk_TargetRate_WB_21[201 - 10] = {
66                                               0,  0,  0,  8, 29, 41,
67      49, 56, 62, 66, 70, 74, 77, 80, 83, 86, 88, 91, 93, 95, 97, 99,
68     101,103,105,107,108,110,112,113,115,116,118,119,121,122,123,125,
69     126,127,129,130,131,132,134,135,136,137,138,140,141,142,143,144,
70     145,146,147,148,149,150,151,152,153,154,156,157,158,159,159,160,
71     161,162,163,164,165,166,167,168,169,170,171,171,172,173,174,175,
72     176,177,177,178,179,180,181,181,182,183,184,185,185,186,187,188,
73     189,189,190,191,192,192,193,194,195,195,196,197,198,198,199,200,
74     200,201,202,203,203,204,205,206,206,207,208,209,209,210,211,211,
75     212,213,214,214,215,216,216,217,218,219,219,220,221,221,222,223,
76     224,224,225,226,226,227,228,229,229,230,231,232,232,233,234,234,
77     235,236,237,237,238,239,240,240,241,242,243,243,244,245,246,246,
78     247,248,249,249,250,251,252,253,255
79 };
80
81 /* Control SNR of redidual quantizer */
82 opus_int silk_control_SNR(
83     silk_encoder_state          *psEncC,                        /* I/O  Pointer to Silk encoder state               */
84     opus_int32                  TargetRate_bps                  /* I    Target max bitrate (bps)                    */
85 )
86 {
87     int id;
88     int bound;
89     const unsigned char *snr_table;
90
91     psEncC->TargetRate_bps = TargetRate_bps;
92     if( psEncC->nb_subfr == 2 ) {
93         TargetRate_bps -= 2000 + psEncC->fs_kHz/16;
94     }
95     if( psEncC->fs_kHz == 8 ) {
96         bound = sizeof(silk_TargetRate_NB_21);
97         snr_table = silk_TargetRate_NB_21;
98     } else if( psEncC->fs_kHz == 12 ) {
99         bound = sizeof(silk_TargetRate_MB_21);
100         snr_table = silk_TargetRate_MB_21;
101     } else {
102         bound = sizeof(silk_TargetRate_WB_21);
103         snr_table = silk_TargetRate_WB_21;
104     }
105     id = (TargetRate_bps+200)/400;
106     id = silk_min(id - 10, bound-1);
107     if( id <= 0 ) {
108         psEncC->SNR_dB_Q7 = 0;
109     } else {
110         psEncC->SNR_dB_Q7 = snr_table[id]*21;
111     }
112     return SILK_NO_ERROR;
113 }