Improving rate control for low bitrate
[opus.git] / silk / control_SNR.c
index 464c1ac..9a6db27 100644 (file)
@@ -32,44 +32,82 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "main.h"
 #include "tuning_parameters.h"
 
+/* These tables hold SNR values divided by 21 (so they fit in 8 bits)
+   for different target bitrates spaced at 400 bps interval. The first
+   10 values are omitted (0-4 kb/s) because they're all zeros.
+   These tables were obtained by running different SNRs through the
+   encoder and measuring the active bitrate. */
+static const unsigned char silk_TargetRate_NB_21[117 - 10] = {
+                                              0, 15, 39, 52, 61, 68,
+     74, 79, 84, 88, 92, 95, 99,102,105,108,111,114,117,119,122,124,
+    126,129,131,133,135,137,139,142,143,145,147,149,151,153,155,157,
+    158,160,162,163,165,167,168,170,171,173,174,176,177,179,180,182,
+    183,185,186,187,189,190,192,193,194,196,197,199,200,201,203,204,
+    205,207,208,209,211,212,213,215,216,217,219,220,221,223,224,225,
+    227,228,230,231,232,234,235,236,238,239,241,242,243,245,246,248,
+    249,250,252,253,255
+};
+
+static const unsigned char silk_TargetRate_MB_21[165 - 10] = {
+                                              0,  0, 28, 43, 52, 59,
+     65, 70, 74, 78, 81, 85, 87, 90, 93, 95, 98,100,102,105,107,109,
+    111,113,115,116,118,120,122,123,125,127,128,130,131,133,134,136,
+    137,138,140,141,143,144,145,147,148,149,151,152,153,154,156,157,
+    158,159,160,162,163,164,165,166,167,168,169,171,172,173,174,175,
+    176,177,178,179,180,181,182,183,184,185,186,187,188,188,189,190,
+    191,192,193,194,195,196,197,198,199,200,201,202,203,203,204,205,
+    206,207,208,209,210,211,212,213,214,214,215,216,217,218,219,220,
+    221,222,223,224,224,225,226,227,228,229,230,231,232,233,234,235,
+    236,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,
+    251,252,253,254,255
+};
+
+static const unsigned char silk_TargetRate_WB_21[201 - 10] = {
+                                              0,  0,  0,  8, 29, 41,
+     49, 56, 62, 66, 70, 74, 77, 80, 83, 86, 88, 91, 93, 95, 97, 99,
+    101,103,105,107,108,110,112,113,115,116,118,119,121,122,123,125,
+    126,127,129,130,131,132,134,135,136,137,138,140,141,142,143,144,
+    145,146,147,148,149,150,151,152,153,154,156,157,158,159,159,160,
+    161,162,163,164,165,166,167,168,169,170,171,171,172,173,174,175,
+    176,177,177,178,179,180,181,181,182,183,184,185,185,186,187,188,
+    189,189,190,191,192,192,193,194,195,195,196,197,198,198,199,200,
+    200,201,202,203,203,204,205,206,206,207,208,209,209,210,211,211,
+    212,213,214,214,215,216,216,217,218,219,219,220,221,221,222,223,
+    224,224,225,226,226,227,228,229,229,230,231,232,232,233,234,234,
+    235,236,237,237,238,239,240,240,241,242,243,243,244,245,246,246,
+    247,248,249,249,250,251,252,253,255
+};
+
 /* Control SNR of redidual quantizer */
 opus_int silk_control_SNR(
     silk_encoder_state          *psEncC,                        /* I/O  Pointer to Silk encoder state               */
     opus_int32                  TargetRate_bps                  /* I    Target max bitrate (bps)                    */
 )
 {
-    opus_int k, ret = SILK_NO_ERROR;
-    opus_int32 frac_Q6;
-    const opus_int32 *rateTable;
-
-    /* Set bitrate/coding quality */
-    TargetRate_bps = silk_LIMIT( TargetRate_bps, MIN_TARGET_RATE_BPS, MAX_TARGET_RATE_BPS );
-    if( TargetRate_bps != psEncC->TargetRate_bps ) {
-        psEncC->TargetRate_bps = TargetRate_bps;
-
-        /* If new TargetRate_bps, translate to SNR_dB value */
-        if( psEncC->fs_kHz == 8 ) {
-            rateTable = silk_TargetRate_table_NB;
-        } else if( psEncC->fs_kHz == 12 ) {
-            rateTable = silk_TargetRate_table_MB;
-        } else {
-            rateTable = silk_TargetRate_table_WB;
-        }
+    int id;
+    int bound;
+    const unsigned char *snr_table;
 
-        /* Reduce bitrate for 10 ms modes in these calculations */
-        if( psEncC->nb_subfr == 2 ) {
-            TargetRate_bps -= REDUCE_BITRATE_10_MS_BPS;
-        }
-
-        /* Find bitrate interval in table and interpolate */
-        for( k = 1; k < TARGET_RATE_TAB_SZ; k++ ) {
-            if( TargetRate_bps <= rateTable[ k ] ) {
-                frac_Q6 = silk_DIV32( silk_LSHIFT( TargetRate_bps - rateTable[ k - 1 ], 6 ), rateTable[ k ] - rateTable[ k - 1 ] );
-                psEncC->SNR_dB_Q7 = silk_LSHIFT( silk_SNR_table_Q1[ k - 1 ], 6 ) + silk_MUL( frac_Q6, silk_SNR_table_Q1[ k ] - silk_SNR_table_Q1[ k - 1 ] );
-                break;
-            }
-        }
+    psEncC->TargetRate_bps = TargetRate_bps;
+    if( psEncC->nb_subfr == 2 ) {
+        TargetRate_bps -= 2000 + psEncC->fs_kHz/16;
     }
-
-    return ret;
+    if( psEncC->fs_kHz == 8 ) {
+        bound = sizeof(silk_TargetRate_NB_21);
+        snr_table = silk_TargetRate_NB_21;
+    } else if( psEncC->fs_kHz == 12 ) {
+        bound = sizeof(silk_TargetRate_MB_21);
+        snr_table = silk_TargetRate_MB_21;
+    } else {
+        bound = sizeof(silk_TargetRate_WB_21);
+        snr_table = silk_TargetRate_WB_21;
+    }
+    id = (TargetRate_bps+200)/400;
+    id = silk_min(id - 10, bound-1);
+    if( id <= 0 ) {
+        psEncC->SNR_dB_Q7 = 0;
+    } else {
+        psEncC->SNR_dB_Q7 = snr_table[id]*21;
+    }
+    return SILK_NO_ERROR;
 }