3 * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
26 * @author Michael Niedermayer <michaelni@gmx.at>
34 #define FILTER_SHIFT 15
37 #define FELEM2 int32_t
38 #define FELEM_MAX INT16_MAX
39 #define FELEM_MIN INT16_MIN
41 #define FILTER_SHIFT 22
44 #define FELEM2 int64_t
45 #define FELEM_MAX INT32_MAX
46 #define FELEM_MIN INT32_MIN
50 typedef struct AVResampleContext{
58 int compensation_distance;
65 * 0th order modified bessel function of the first kind.
67 static double bessel(double x){
74 v += pow(x*x/4, i)/(t*t);
80 * builds a polyphase filterbank.
81 * @param factor resampling factor
82 * @param scale wanted sum of coefficients for each filter
83 * @param type 0->cubic, 1->blackman nuttall windowed sinc, 2->kaiser windowed sinc beta=16
85 void av_build_filter(FELEM *filter, double factor, int tap_count, int phase_count, int scale, int type){
87 double x, y, w, tab[tap_count];
88 const int center= (tap_count-1)/2;
90 /* if upsampling, only need to interpolate, no filter */
94 for(ph=0;ph<phase_count;ph++) {
96 for(i=0;i<tap_count;i++) {
97 x = M_PI * ((double)(i - center) - (double)ph / phase_count) * factor;
102 const float d= -0.5; //first order derivative = -0.5
103 x = fabs(((double)(i - center) - (double)ph / phase_count) * factor);
104 if(x<1.0) y= 1 - 3*x*x + 2*x*x*x + d*( -x*x + x*x*x);
105 else y= d*(-4 + 8*x - 5*x*x + x*x*x);
108 w = 2.0*x / (factor*tap_count) + M_PI;
109 y *= 0.3635819 - 0.4891775 * cos(w) + 0.1365995 * cos(2*w) - 0.0106411 * cos(3*w);
112 w = 2.0*x / (factor*tap_count*M_PI);
113 y *= bessel(16*sqrt(FFMAX(1-w*w, 0)));
121 /* normalize so that an uniform color remains the same */
122 for(i=0;i<tap_count;i++) {
123 v = av_clip(lrintf(tab[i] * scale / norm), FELEM_MIN, FELEM_MAX);
124 filter[ph * tap_count + i] = v;
131 double sine[LEN + tap_count];
132 double filtered[LEN];
133 double maxff=-2, minff=2, maxsf=-2, minsf=2;
134 for(i=0; i<LEN; i++){
135 double ss=0, sf=0, ff=0;
136 for(j=0; j<LEN+tap_count; j++)
137 sine[j]= cos(i*j*M_PI/LEN);
138 for(j=0; j<LEN; j++){
141 for(k=0; k<tap_count; k++)
142 sum += filter[ph * tap_count + k] * sine[k+j];
143 filtered[j]= sum / (1<<FILTER_SHIFT);
144 ss+= sine[j + center] * sine[j + center];
145 ff+= filtered[j] * filtered[j];
146 sf+= sine[j + center] * filtered[j];
151 maxff= FFMAX(maxff, ff);
152 minff= FFMIN(minff, ff);
153 maxsf= FFMAX(maxsf, sf);
154 minsf= FFMIN(minsf, sf);
156 av_log(NULL, AV_LOG_ERROR, "i:%4d ss:%f ff:%f-%f sf:%f-%f\n", i, ss, maxff, minff, maxsf, minsf);
166 * initalizes a audio resampler.
167 * note, if either rate is not a integer then simply scale both rates up so they are
169 AVResampleContext *av_resample_init(int out_rate, int in_rate, int filter_size, int phase_shift, int linear, double cutoff){
170 AVResampleContext *c= av_mallocz(sizeof(AVResampleContext));
171 double factor= FFMIN(out_rate * cutoff / in_rate, 1.0);
172 int phase_count= 1<<phase_shift;
174 c->phase_shift= phase_shift;
175 c->phase_mask= phase_count-1;
178 c->filter_length= FFMAX((int)ceil(filter_size/factor), 1);
179 c->filter_bank= av_mallocz(c->filter_length*(phase_count+1)*sizeof(FELEM));
180 av_build_filter(c->filter_bank, factor, c->filter_length, phase_count, 1<<FILTER_SHIFT, 1);
181 memcpy(&c->filter_bank[c->filter_length*phase_count+1], c->filter_bank, (c->filter_length-1)*sizeof(FELEM));
182 c->filter_bank[c->filter_length*phase_count]= c->filter_bank[c->filter_length - 1];
184 c->src_incr= out_rate;
185 c->ideal_dst_incr= c->dst_incr= in_rate * phase_count;
186 c->index= -phase_count*((c->filter_length-1)/2);
191 void av_resample_close(AVResampleContext *c){
192 av_freep(&c->filter_bank);
197 * Compensates samplerate/timestamp drift. The compensation is done by changing
198 * the resampler parameters, so no audible clicks or similar distortions ocur
199 * @param compensation_distance distance in output samples over which the compensation should be performed
200 * @param sample_delta number of output samples which should be output less
202 * example: av_resample_compensate(c, 10, 500)
203 * here instead of 510 samples only 500 samples would be output
205 * note, due to rounding the actual compensation might be slightly different,
206 * especially if the compensation_distance is large and the in_rate used during init is small
208 void av_resample_compensate(AVResampleContext *c, int sample_delta, int compensation_distance){
209 // sample_delta += (c->ideal_dst_incr - c->dst_incr)*(int64_t)c->compensation_distance / c->ideal_dst_incr;
210 c->compensation_distance= compensation_distance;
211 c->dst_incr = c->ideal_dst_incr - c->ideal_dst_incr * (int64_t)sample_delta / compensation_distance;
216 * @param src an array of unconsumed samples
217 * @param consumed the number of samples of src which have been consumed are returned here
218 * @param src_size the number of unconsumed samples available
219 * @param dst_size the amount of space in samples available in dst
220 * @param update_ctx if this is 0 then the context wont be modified, that way several channels can be resampled with the same context
221 * @return the number of samples written in dst or -1 if an error occured
223 int av_resample(AVResampleContext *c, short *dst, short *src, int *consumed, int src_size, int dst_size, int update_ctx){
227 int dst_incr_frac= c->dst_incr % c->src_incr;
228 int dst_incr= c->dst_incr / c->src_incr;
229 int compensation_distance= c->compensation_distance;
231 if(compensation_distance == 0 && c->filter_length == 1 && c->phase_shift==0){
232 int64_t index2= ((int64_t)index)<<32;
233 int64_t incr= (1LL<<32) * c->dst_incr / c->src_incr;
234 dst_size= FFMIN(dst_size, (src_size-1-index) * (int64_t)c->src_incr / c->dst_incr);
236 for(dst_index=0; dst_index < dst_size; dst_index++){
237 dst[dst_index] = src[index2>>32];
240 frac += dst_index * dst_incr_frac;
241 index += dst_index * dst_incr;
242 index += frac / c->src_incr;
245 for(dst_index=0; dst_index < dst_size; dst_index++){
246 FELEM *filter= c->filter_bank + c->filter_length*(index & c->phase_mask);
247 int sample_index= index >> c->phase_shift;
250 if(sample_index < 0){
251 for(i=0; i<c->filter_length; i++)
252 val += src[FFABS(sample_index + i) % src_size] * filter[i];
253 }else if(sample_index + c->filter_length > src_size){
257 int sub_phase= (frac<<8) / c->src_incr;
258 for(i=0; i<c->filter_length; i++){
259 int64_t coeff= filter[i]*(256 - sub_phase) + filter[i + c->filter_length]*sub_phase;
260 v += src[sample_index + i] * coeff;
264 for(i=0; i<c->filter_length; i++){
265 val += src[sample_index + i] * (FELEM2)filter[i];
269 val = (val + (1<<(FILTER_SHIFT-1)))>>FILTER_SHIFT;
270 dst[dst_index] = (unsigned)(val + 32768) > 65535 ? (val>>31) ^ 32767 : val;
272 frac += dst_incr_frac;
274 if(frac >= c->src_incr){
279 if(dst_index + 1 == compensation_distance){
280 compensation_distance= 0;
281 dst_incr_frac= c->ideal_dst_incr % c->src_incr;
282 dst_incr= c->ideal_dst_incr / c->src_incr;
286 *consumed= FFMAX(index, 0) >> c->phase_shift;
287 if(index>=0) index &= c->phase_mask;
289 if(compensation_distance){
290 compensation_distance -= dst_index;
291 assert(compensation_distance > 0);
296 c->dst_incr= dst_incr_frac + c->src_incr*dst_incr;
297 c->compensation_distance= compensation_distance;
300 if(update_ctx && !c->compensation_distance){
302 av_resample_compensate(c, rand() % (8000*2) - 8000, 8000*2);
303 av_log(NULL, AV_LOG_DEBUG, "%d %d %d\n", c->dst_incr, c->ideal_dst_incr, c->compensation_distance);