Interesting Audio Filters for MPlayer

af_alternate.c

/*
 * Copyright (C) 2012 Xidorn Quan <quanxunzhen@gmail.com>
 *
 * This file is part of MPlayer.
 *
 * MPlayer 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.
 *
 * MPlayer 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 MPlayer; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <stdlib.h>
#include <assert.h>
#include <inttypes.h>
#include <limits.h>
#include <math.h>

#include "mp_msg.h"
#include "af.h"

#ifndef M_PI
#   define M_PI 3.141592653589793
#endif

typedef struct af_alternate_s
{
    float freq;
    float amin, amax;
    float pos;
} af_alternate_t;

static int control(af_instance_t *af, int cmd, void *arg)
{
    af_data_t *data;
    af_alternate_t *s = af->setup;
    float period;

    switch (cmd) {
    case AF_CONTROL_REINIT:
        if (!arg) return AF_ERROR;
        data = arg;
        af->data->rate = data->rate;
        af->data->nch = 2;
        af->data->format = AF_FORMAT_FLOAT_NE;
        af->data->bps = 4;
        return af_test_output(af, data);
    case AF_CONTROL_COMMAND_LINE:
        sscanf((char *)arg, "%f:%f:%f",
                &period, &s->amin, &s->amax);
        s->freq = 1.0 / period;
        return AF_OK;
    }
    return AF_UNKNOWN;
}

static void uninit(af_instance_t *af)
{
    free(af->data);
    free(af->setup);
}

static af_data_t *play(af_instance_t *af, af_data_t *data)
{
    af_alternate_t *s = af->setup;
    double pos = s->pos;
    int rate = af->data->rate;
    float freq = s->freq;
    float amin = s->amin, amax = s->amax,
          aspan = (amax - amin) / 2;
    size_t i, ch;

    float *a = data->audio;
    int len = data->len / 4;
    for (i = 0; i < len / 2; i++) {
        float x = sin(pos) * aspan;
        pos += freq * M_PI * 2 / rate;
        for (ch = 0; ch < 2; ch++) {
            size_t p = i * 2 + ch;
            float t = a[p] * (amin + aspan + x * (ch ? -1 : 1));
            a[p] = clamp(t, -1.0, 1.0);
        }
    }
    pos -= floor(pos / (M_PI * 2)) * M_PI * 2;
    s->pos = pos;
    return data;
}

static int af_open(af_instance_t *af)
{
    af_alternate_t *s;
    af->control = control;
    af->uninit = uninit;
    af->play = play;
    af->mul = 1.0f;
    af->data = calloc(1, sizeof(af_data_t));
    af->setup = s = calloc(1, sizeof(af_alternate_t));
    if (!af->data || !af->setup)
        return AF_ERROR;
    s->freq = 0.2;
    s->amin = 0.0;
    s->amax = 1.0;
    s->pos = 0.0;
    return AF_OK;
}

af_info_t af_info_alternate = {
    "Alternating sound between two channals",
    "alternate",
    "Xidorn",
    "",
    AF_FLAGS_NOT_REENTRANT,
    af_open
};

changes.diff

Index: Makefile
===================================================================
--- Makefile	(revision 35239)
+++ Makefile	(working copy)
@@ -322,6 +322,7 @@
               libaf/af_tools.c \
               libaf/af_volnorm.c \
               libaf/af_volume.c \
+              libaf/af_alternate.c \
               libaf/filter.c \
               libaf/format.c \
               libaf/reorder_ch.c \
Index: libaf/af.c
===================================================================
--- libaf/af.c	(revision 35239)
+++ libaf/af.c	(working copy)
@@ -53,6 +53,7 @@
 extern const af_info_t af_info_scaletempo;
 extern const af_info_t af_info_stats;
 extern const af_info_t af_info_bs2b;
+extern const af_info_t af_info_alternate;
 
 static const af_info_t * const filter_list[] = {
    &af_info_dummy,
@@ -89,6 +90,7 @@
 #ifdef CONFIG_LIBBS2B
    &af_info_bs2b,
 #endif
+   &af_info_alternate,
    NULL
 };