/* * Sample rate convertion for both audio and video * Copyright (c) 2000 Gerard Lantau. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #include "avcodec.h" #include <math.h> typedef struct { /* fractional resampling */ UINT32 incr; /* fractional increment */ UINT32 frac; int last_sample; /* integer down sample */ int iratio; /* integer divison ratio */ int icount, isum; int inv; } ReSampleChannelContext; struct ReSampleContext { ReSampleChannelContext channel_ctx[2]; float ratio; /* channel convert */ int input_channels, output_channels, filter_channels; }; #define FRAC_BITS 16 #define FRAC (1 << FRAC_BITS) static void init_mono_resample(ReSampleChannelContext *s, float ratio) { ratio = 1.0 / ratio; s->iratio = (int)floor(ratio); if (s->iratio == 0) s->iratio = 1; s->incr = (int)((ratio / s->iratio) * FRAC); s->frac = 0; s->last_sample = 0; s->icount = s->iratio; s->isum = 0; s->inv = (FRAC / s->iratio); } /* fractional audio resampling */ static int fractional_resample(ReSampleChannelContext *s, short *output, short *input, int nb_samples) { unsigned int frac, incr; int l0, l1; short *q, *p, *pend; l0 = s->last_sample; incr = s->incr; frac = s->frac; p = input; pend = input + nb_samples; q = output; l1 = *p++; for(;;) { /* interpolate */ *q++ = (l0 * (FRAC - frac) + l1 * frac) >> FRAC_BITS; frac = frac + s->incr; while (frac >= FRAC) { if (p >= pend) goto the_end; frac -= FRAC; l0 = l1; l1 = *p++; } } the_end: s->last_sample = l1; s->frac = frac; return q - output; } static int integer_downsample(ReSampleChannelContext *s, short *output, short *input, int nb_samples) { short *q, *p, *pend; int c, sum; p = input; pend = input + nb_samples; q = output; c = s->icount; sum = s->isum; for(;;) { sum += *p++; if (--c == 0) { *q++ = (sum * s->inv) >> FRAC_BITS; c = s->iratio; sum = 0; } if (p >= pend) break; } s->isum = sum; s->icount = c; return q - output; } /* n1: number of samples */ static void stereo_to_mono(short *output, short *input, int n1) { short *p, *q; int n = n1; p = input; q = output; while (n >= 4) { q[0] = (p[0] + p[1]) >> 1; q[1] = (p[2] + p[3]) >> 1; q[2] = (p[4] + p[5]) >> 1; q[3] = (p[6] + p[7]) >> 1; q += 4; p += 8; n -= 4; } while (n > 0) { q[0] = (p[0] + p[1]) >> 1; q++; p += 2; n--; } } /* n1: number of samples */ static void mono_to_stereo(short *output, short *input, int n1) { short *p, *q; int n = n1; int v; p = input; q = output; while (n >= 4) { v = p[0]; q[0] = v; q[1] = v; v = p[1]; q[2] = v; q[3] = v; v = p[2]; q[4] = v; q[5] = v; v = p[3]; q[6] = v; q[7] = v; q += 8; p += 4; n -= 4; } while (n > 0) { v = p[0]; q[0] = v; q[1] = v; q += 2; p += 1; n--; } } /* XXX: should use more abstract 'N' channels system */ static void stereo_split(short *output1, short *output2, short *input, int n) { int i; for(i=0;i<n;i++) { *output1++ = *input++; *output2++ = *input++; } } static void stereo_mux(short *output, short *input1, short *input2, int n) { int i; for(i=0;i<n;i++) { *output++ = *input1++; *output++ = *input2++; } } static int mono_resample(ReSampleChannelContext *s, short *output, short *input, int nb_samples) { short *buf1; short *buftmp; buf1= (short*) malloc( nb_samples * sizeof(short) ); /* first downsample by an integer factor with averaging filter */ if (s->iratio > 1) { buftmp = buf1; nb_samples = integer_downsample(s, buftmp, input, nb_samples); } else { buftmp = input; } /* then do a fractional resampling with linear interpolation */ if (s->incr != FRAC) { nb_samples = fractional_resample(s, output, buftmp, nb_samples); } else { memcpy(output, buftmp, nb_samples * sizeof(short)); } free(buf1); return nb_samples; } ReSampleContext *audio_resample_init(int output_channels, int input_channels, int output_rate, int input_rate) { ReSampleContext *s; int i; if (output_channels > 2 || input_channels > 2) return NULL; s = av_mallocz(sizeof(ReSampleContext)); if (!s) return NULL; s->ratio = (float)output_rate / (float)input_rate; s->input_channels = input_channels; s->output_channels = output_channels; s->filter_channels = s->input_channels; if (s->output_channels < s->filter_channels) s->filter_channels = s->output_channels; for(i=0;i<s->filter_channels;i++) { init_mono_resample(&s->channel_ctx[i], s->ratio); } return s; } /* resample audio. 'nb_samples' is the number of input samples */ /* XXX: optimize it ! */ /* XXX: do it with polyphase filters, since the quality here is HORRIBLE. Return the number of samples available in output */ int audio_resample(ReSampleContext *s, short *output, short *input, int nb_samples) { int i, nb_samples1; short *bufin[2]; short *bufout[2]; short *buftmp2[2], *buftmp3[2]; int lenout; if (s->input_channels == s->output_channels && s->ratio == 1.0) { /* nothing to do */ memcpy(output, input, nb_samples * s->input_channels * sizeof(short)); return nb_samples; } /* XXX: move those malloc to resample init code */ bufin[0]= (short*) malloc( nb_samples * sizeof(short) ); bufin[1]= (short*) malloc( nb_samples * sizeof(short) ); /* make some zoom to avoid round pb */ lenout= (int)(nb_samples * s->ratio) + 16; bufout[0]= (short*) malloc( lenout * sizeof(short) ); bufout[1]= (short*) malloc( lenout * sizeof(short) ); if (s->input_channels == 2 && s->output_channels == 1) { buftmp2[0] = bufin[0]; buftmp3[0] = output; stereo_to_mono(buftmp2[0], input, nb_samples); } else if (s->output_channels == 2 && s->input_channels == 1) { buftmp2[0] = input; buftmp3[0] = bufout[0]; } else if (s->output_channels == 2) { buftmp2[0] = bufin[0]; buftmp2[1] = bufin[1]; buftmp3[0] = bufout[0]; buftmp3[1] = bufout[1]; stereo_split(buftmp2[0], buftmp2[1], input, nb_samples); } else { buftmp2[0] = input; buftmp3[0] = output; } /* resample each channel */ nb_samples1 = 0; /* avoid warning */ for(i=0;i<s->filter_channels;i++) { nb_samples1 = mono_resample(&s->channel_ctx[i], buftmp3[i], buftmp2[i], nb_samples); } if (s->output_channels == 2 && s->input_channels == 1) { mono_to_stereo(output, buftmp3[0], nb_samples1); } else if (s->output_channels == 2) { stereo_mux(output, buftmp3[0], buftmp3[1], nb_samples1); } free(bufin[0]); free(bufin[1]); free(bufout[0]); free(bufout[1]); return nb_samples1; } void audio_resample_close(ReSampleContext *s) { free(s); }