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Improving rate control for low bitrate
Using a finer table for the rate to SNR curves in silk_control_SNR(). It's now possible to have an SNR that reaches 0, so we can lower bitrate down to ~5 kbps for narrowband and 5.5 kbps for wideband.
This commit is contained in:
Jean-Marc Valin
parent
004ef8b9b1
commit
85ce87ffbe
4 changed files with 70 additions and 53 deletions
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@ -32,44 +32,82 @@ POSSIBILITY OF SUCH DAMAGE.
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#include "main.h"
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#include "main.h"
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#include "tuning_parameters.h"
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#include "tuning_parameters.h"
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/* These tables hold SNR values divided by 21 (so they fit in 8 bits)
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for different target bitrates spaced at 400 bps interval. The first
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10 values are omitted (0-4 kb/s) because they're all zeros.
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These tables were obtained by running different SNRs through the
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encoder and measuring the active bitrate. */
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static const unsigned char silk_TargetRate_NB_21[117 - 10] = {
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0, 15, 39, 52, 61, 68,
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74, 79, 84, 88, 92, 95, 99,102,105,108,111,114,117,119,122,124,
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126,129,131,133,135,137,139,142,143,145,147,149,151,153,155,157,
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158,160,162,163,165,167,168,170,171,173,174,176,177,179,180,182,
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183,185,186,187,189,190,192,193,194,196,197,199,200,201,203,204,
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205,207,208,209,211,212,213,215,216,217,219,220,221,223,224,225,
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227,228,230,231,232,234,235,236,238,239,241,242,243,245,246,248,
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249,250,252,253,255
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};
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static const unsigned char silk_TargetRate_MB_21[165 - 10] = {
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0, 0, 28, 43, 52, 59,
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65, 70, 74, 78, 81, 85, 87, 90, 93, 95, 98,100,102,105,107,109,
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111,113,115,116,118,120,122,123,125,127,128,130,131,133,134,136,
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137,138,140,141,143,144,145,147,148,149,151,152,153,154,156,157,
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158,159,160,162,163,164,165,166,167,168,169,171,172,173,174,175,
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176,177,178,179,180,181,182,183,184,185,186,187,188,188,189,190,
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191,192,193,194,195,196,197,198,199,200,201,202,203,203,204,205,
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206,207,208,209,210,211,212,213,214,214,215,216,217,218,219,220,
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221,222,223,224,224,225,226,227,228,229,230,231,232,233,234,235,
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236,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,
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251,252,253,254,255
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};
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static const unsigned char silk_TargetRate_WB_21[201 - 10] = {
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0, 0, 0, 8, 29, 41,
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49, 56, 62, 66, 70, 74, 77, 80, 83, 86, 88, 91, 93, 95, 97, 99,
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101,103,105,107,108,110,112,113,115,116,118,119,121,122,123,125,
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126,127,129,130,131,132,134,135,136,137,138,140,141,142,143,144,
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145,146,147,148,149,150,151,152,153,154,156,157,158,159,159,160,
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161,162,163,164,165,166,167,168,169,170,171,171,172,173,174,175,
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176,177,177,178,179,180,181,181,182,183,184,185,185,186,187,188,
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189,189,190,191,192,192,193,194,195,195,196,197,198,198,199,200,
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200,201,202,203,203,204,205,206,206,207,208,209,209,210,211,211,
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212,213,214,214,215,216,216,217,218,219,219,220,221,221,222,223,
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224,224,225,226,226,227,228,229,229,230,231,232,232,233,234,234,
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235,236,237,237,238,239,240,240,241,242,243,243,244,245,246,246,
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247,248,249,249,250,251,252,253,255
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};
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/* Control SNR of redidual quantizer */
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/* Control SNR of redidual quantizer */
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opus_int silk_control_SNR(
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opus_int silk_control_SNR(
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silk_encoder_state *psEncC, /* I/O Pointer to Silk encoder state */
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silk_encoder_state *psEncC, /* I/O Pointer to Silk encoder state */
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opus_int32 TargetRate_bps /* I Target max bitrate (bps) */
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opus_int32 TargetRate_bps /* I Target max bitrate (bps) */
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)
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)
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{
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{
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opus_int k, ret = SILK_NO_ERROR;
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int id;
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opus_int32 frac_Q6;
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int bound;
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const opus_int32 *rateTable;
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const unsigned char *snr_table;
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/* Set bitrate/coding quality */
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psEncC->TargetRate_bps = TargetRate_bps;
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TargetRate_bps = silk_LIMIT( TargetRate_bps, MIN_TARGET_RATE_BPS, MAX_TARGET_RATE_BPS );
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if( psEncC->nb_subfr == 2 ) {
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if( TargetRate_bps != psEncC->TargetRate_bps ) {
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TargetRate_bps -= 2000 + psEncC->fs_kHz/16;
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psEncC->TargetRate_bps = TargetRate_bps;
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/* If new TargetRate_bps, translate to SNR_dB value */
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if( psEncC->fs_kHz == 8 ) {
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rateTable = silk_TargetRate_table_NB;
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} else if( psEncC->fs_kHz == 12 ) {
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rateTable = silk_TargetRate_table_MB;
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} else {
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rateTable = silk_TargetRate_table_WB;
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}
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/* Reduce bitrate for 10 ms modes in these calculations */
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if( psEncC->nb_subfr == 2 ) {
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TargetRate_bps -= REDUCE_BITRATE_10_MS_BPS;
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}
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/* Find bitrate interval in table and interpolate */
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for( k = 1; k < TARGET_RATE_TAB_SZ; k++ ) {
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if( TargetRate_bps <= rateTable[ k ] ) {
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frac_Q6 = silk_DIV32( silk_LSHIFT( TargetRate_bps - rateTable[ k - 1 ], 6 ), rateTable[ k ] - rateTable[ k - 1 ] );
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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 ] );
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break;
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}
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}
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}
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}
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if( psEncC->fs_kHz == 8 ) {
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return ret;
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bound = sizeof(silk_TargetRate_NB_21);
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snr_table = silk_TargetRate_NB_21;
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} else if( psEncC->fs_kHz == 12 ) {
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bound = sizeof(silk_TargetRate_MB_21);
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snr_table = silk_TargetRate_MB_21;
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} else {
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bound = sizeof(silk_TargetRate_WB_21);
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snr_table = silk_TargetRate_WB_21;
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}
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id = (TargetRate_bps+200)/400;
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id = silk_min(id - 10, bound-1);
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if( id <= 0 ) {
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psEncC->SNR_dB_Q7 = 0;
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} else {
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psEncC->SNR_dB_Q7 = snr_table[id]*21;
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}
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return SILK_NO_ERROR;
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}
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}
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@ -46,7 +46,6 @@ extern "C"
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/* Limits on bitrate */
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/* Limits on bitrate */
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#define MIN_TARGET_RATE_BPS 5000
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#define MIN_TARGET_RATE_BPS 5000
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#define MAX_TARGET_RATE_BPS 80000
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#define MAX_TARGET_RATE_BPS 80000
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#define TARGET_RATE_TAB_SZ 8
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/* LBRR thresholds */
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/* LBRR thresholds */
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#define LBRR_NB_MIN_RATE_BPS 12000
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#define LBRR_NB_MIN_RATE_BPS 12000
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@ -97,12 +97,6 @@ extern const opus_uint8 silk_NLSF_interpolation_factor_iCDF[ 5 ];
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extern const silk_NLSF_CB_struct silk_NLSF_CB_WB; /* 1040 */
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extern const silk_NLSF_CB_struct silk_NLSF_CB_WB; /* 1040 */
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extern const silk_NLSF_CB_struct silk_NLSF_CB_NB_MB; /* 728 */
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extern const silk_NLSF_CB_struct silk_NLSF_CB_NB_MB; /* 728 */
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/* Piece-wise linear mapping from bitrate in kbps to coding quality in dB SNR */
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extern const opus_int32 silk_TargetRate_table_NB[ TARGET_RATE_TAB_SZ ]; /* 32 */
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extern const opus_int32 silk_TargetRate_table_MB[ TARGET_RATE_TAB_SZ ]; /* 32 */
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extern const opus_int32 silk_TargetRate_table_WB[ TARGET_RATE_TAB_SZ ]; /* 32 */
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extern const opus_int16 silk_SNR_table_Q1[ TARGET_RATE_TAB_SZ ]; /* 32 */
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/* Quantization offsets */
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/* Quantization offsets */
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extern const opus_int16 silk_Quantization_Offsets_Q10[ 2 ][ 2 ]; /* 8 */
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extern const opus_int16 silk_Quantization_Offsets_Q10[ 2 ][ 2 ]; /* 8 */
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@ -38,20 +38,6 @@ extern "C"
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{
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{
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#endif
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#endif
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/* Piece-wise linear mapping from bitrate in kbps to coding quality in dB SNR */
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const opus_int32 silk_TargetRate_table_NB[ TARGET_RATE_TAB_SZ ] = {
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0, 8000, 9400, 11500, 13500, 17500, 25000, MAX_TARGET_RATE_BPS
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};
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const opus_int32 silk_TargetRate_table_MB[ TARGET_RATE_TAB_SZ ] = {
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0, 9000, 12000, 14500, 18500, 24500, 35500, MAX_TARGET_RATE_BPS
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};
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const opus_int32 silk_TargetRate_table_WB[ TARGET_RATE_TAB_SZ ] = {
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0, 10500, 14000, 17000, 21500, 28500, 42000, MAX_TARGET_RATE_BPS
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};
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const opus_int16 silk_SNR_table_Q1[ TARGET_RATE_TAB_SZ ] = {
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18, 29, 38, 40, 46, 52, 62, 84
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};
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/* Tables for stereo predictor coding */
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/* Tables for stereo predictor coding */
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const opus_int16 silk_stereo_pred_quant_Q13[ STEREO_QUANT_TAB_SIZE ] = {
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const opus_int16 silk_stereo_pred_quant_Q13[ STEREO_QUANT_TAB_SIZE ] = {
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-13732, -10050, -8266, -7526, -6500, -5000, -2950, -820,
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-13732, -10050, -8266, -7526, -6500, -5000, -2950, -820,
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