FFmpeg/libavfilter/avf_showfreqs.c

/*
 * Copyright (c) 2015 Paul B Mahol
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <float.h>
#include <math.h>

#include "libavcodec/avfft.h"
#include "libavutil/audio_fifo.h"
#include "libavutil/avassert.h"
#include "libavutil/avstring.h"
#include "libavutil/channel_layout.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/opt.h"
#include "libavutil/parseutils.h"
#include "audio.h"
#include "video.h"
#include "avfilter.h"
#include "internal.h"
#include "window_func.h"

enum DisplayMode    { LINE, BAR, DOT, NB_MODES };
enum ChannelMode    { COMBINED, SEPARATE, NB_CMODES };
enum FrequencyScale { FS_LINEAR, FS_LOG, FS_RLOG, NB_FSCALES };
enum AmplitudeScale { AS_LINEAR, AS_SQRT, AS_CBRT, AS_LOG, NB_ASCALES };

typedef struct ShowFreqsContext {
    const AVClass *class;
    int w, h;
    int mode;
    int cmode;
    int fft_bits;
    int ascale, fscale;
    int avg;
    int win_func;
    FFTContext *fft;
    FFTComplex **fft_data;
    float **avg_data;
    float *window_func_lut;
    float overlap;
    float minamp;
    int hop_size;
    int nb_channels;
    int nb_freq;
    int win_size;
    float scale;
    char *colors;
    AVAudioFifo *fifo;
    int64_t pts;
} ShowFreqsContext;

#define OFFSET(x) offsetof(ShowFreqsContext, x)
#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM

static const AVOption showfreqs_options[] = {
    { "size", "set video size", OFFSET(w), AV_OPT_TYPE_IMAGE_SIZE, {.str = "1024x512"}, 0, 0, FLAGS },
    { "s",    "set video size", OFFSET(w), AV_OPT_TYPE_IMAGE_SIZE, {.str = "1024x512"}, 0, 0, FLAGS },
    { "mode", "set display mode", OFFSET(mode), AV_OPT_TYPE_INT, {.i64=BAR}, 0, NB_MODES-1, FLAGS, "mode" },
        { "line", "show lines",  0, AV_OPT_TYPE_CONST, {.i64=LINE},   0, 0, FLAGS, "mode" },
        { "bar",  "show bars",   0, AV_OPT_TYPE_CONST, {.i64=BAR},    0, 0, FLAGS, "mode" },
        { "dot",  "show dots",   0, AV_OPT_TYPE_CONST, {.i64=DOT},    0, 0, FLAGS, "mode" },
    { "ascale", "set amplitude scale", OFFSET(ascale), AV_OPT_TYPE_INT, {.i64=AS_LOG}, 0, NB_ASCALES-1, FLAGS, "ascale" },
        { "lin",  "linear",      0, AV_OPT_TYPE_CONST, {.i64=AS_LINEAR}, 0, 0, FLAGS, "ascale" },
        { "sqrt", "square root", 0, AV_OPT_TYPE_CONST, {.i64=AS_SQRT},   0, 0, FLAGS, "ascale" },
        { "cbrt", "cubic root",  0, AV_OPT_TYPE_CONST, {.i64=AS_CBRT},   0, 0, FLAGS, "ascale" },
        { "log",  "logarithmic", 0, AV_OPT_TYPE_CONST, {.i64=AS_LOG},    0, 0, FLAGS, "ascale" },
    { "fscale", "set frequency scale", OFFSET(fscale), AV_OPT_TYPE_INT, {.i64=FS_LINEAR}, 0, NB_FSCALES-1, FLAGS, "fscale" },
        { "lin",  "linear",              0, AV_OPT_TYPE_CONST, {.i64=FS_LINEAR}, 0, 0, FLAGS, "fscale" },
        { "log",  "logarithmic",         0, AV_OPT_TYPE_CONST, {.i64=FS_LOG},    0, 0, FLAGS, "fscale" },
        { "rlog", "reverse logarithmic", 0, AV_OPT_TYPE_CONST, {.i64=FS_RLOG},   0, 0, FLAGS, "fscale" },
    { "win_size", "set window size", OFFSET(fft_bits), AV_OPT_TYPE_INT, {.i64=11}, 4, 16, FLAGS, "fft" },
        { "w16",    0, 0, AV_OPT_TYPE_CONST, {.i64=4},  0, 0, FLAGS, "fft" },
        { "w32",    0, 0, AV_OPT_TYPE_CONST, {.i64=5},  0, 0, FLAGS, "fft" },
        { "w64",    0, 0, AV_OPT_TYPE_CONST, {.i64=6},  0, 0, FLAGS, "fft" },
        { "w128",   0, 0, AV_OPT_TYPE_CONST, {.i64=7},  0, 0, FLAGS, "fft" },
        { "w256",   0, 0, AV_OPT_TYPE_CONST, {.i64=8},  0, 0, FLAGS, "fft" },
        { "w512",   0, 0, AV_OPT_TYPE_CONST, {.i64=9},  0, 0, FLAGS, "fft" },
        { "w1024",  0, 0, AV_OPT_TYPE_CONST, {.i64=10}, 0, 0, FLAGS, "fft" },
        { "w2048",  0, 0, AV_OPT_TYPE_CONST, {.i64=11}, 0, 0, FLAGS, "fft" },
        { "w4096",  0, 0, AV_OPT_TYPE_CONST, {.i64=12}, 0, 0, FLAGS, "fft" },
        { "w8192",  0, 0, AV_OPT_TYPE_CONST, {.i64=13}, 0, 0, FLAGS, "fft" },
        { "w16384", 0, 0, AV_OPT_TYPE_CONST, {.i64=14}, 0, 0, FLAGS, "fft" },
        { "w32768", 0, 0, AV_OPT_TYPE_CONST, {.i64=15}, 0, 0, FLAGS, "fft" },
        { "w65536", 0, 0, AV_OPT_TYPE_CONST, {.i64=16}, 0, 0, FLAGS, "fft" },
    { "win_func", "set window function", OFFSET(win_func), AV_OPT_TYPE_INT, {.i64=WFUNC_HANNING}, 0, NB_WFUNC-1, FLAGS, "win_func" },
        { "rect",     "Rectangular",      0, AV_OPT_TYPE_CONST, {.i64=WFUNC_RECT},     0, 0, FLAGS, "win_func" },
        { "bartlett", "Bartlett",         0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BARTLETT}, 0, 0, FLAGS, "win_func" },
        { "hanning",  "Hanning",          0, AV_OPT_TYPE_CONST, {.i64=WFUNC_HANNING},  0, 0, FLAGS, "win_func" },
        { "hamming",  "Hamming",          0, AV_OPT_TYPE_CONST, {.i64=WFUNC_HAMMING},  0, 0, FLAGS, "win_func" },
        { "blackman", "Blackman",         0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BLACKMAN}, 0, 0, FLAGS, "win_func" },
        { "welch",    "Welch",            0, AV_OPT_TYPE_CONST, {.i64=WFUNC_WELCH},    0, 0, FLAGS, "win_func" },
        { "flattop",  "Flat-top",         0, AV_OPT_TYPE_CONST, {.i64=WFUNC_FLATTOP},  0, 0, FLAGS, "win_func" },
        { "bharris",  "Blackman-Harris",  0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BHARRIS},  0, 0, FLAGS, "win_func" },
        { "bnuttall", "Blackman-Nuttall", 0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BNUTTALL}, 0, 0, FLAGS, "win_func" },
        { "bhann",    "Bartlett-Hann",    0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BHANN},    0, 0, FLAGS, "win_func" },
        { "sine",     "Sine",             0, AV_OPT_TYPE_CONST, {.i64=WFUNC_SINE},     0, 0, FLAGS, "win_func" },
        { "nuttall",  "Nuttall",          0, AV_OPT_TYPE_CONST, {.i64=WFUNC_NUTTALL},  0, 0, FLAGS, "win_func" },
        { "lanczos",  "Lanczos",          0, AV_OPT_TYPE_CONST, {.i64=WFUNC_LANCZOS},  0, 0, FLAGS, "win_func" },
        { "gauss",    "Gauss",            0, AV_OPT_TYPE_CONST, {.i64=WFUNC_GAUSS},    0, 0, FLAGS, "win_func" },
        { "tukey",    "Tukey",            0, AV_OPT_TYPE_CONST, {.i64=WFUNC_TUKEY},    0, 0, FLAGS, "win_func" },
        { "dolph",    "Dolph-Chebyshev",  0, AV_OPT_TYPE_CONST, {.i64=WFUNC_DOLPH},    0, 0, FLAGS, "win_func" },
        { "cauchy",   "Cauchy",           0, AV_OPT_TYPE_CONST, {.i64=WFUNC_CAUCHY},   0, 0, FLAGS, "win_func" },
        { "parzen",   "Parzen",           0, AV_OPT_TYPE_CONST, {.i64=WFUNC_PARZEN},   0, 0, FLAGS, "win_func" },
        { "poisson",  "Poisson",          0, AV_OPT_TYPE_CONST, {.i64=WFUNC_POISSON},  0, 0, FLAGS, "win_func" },
        { "bohman",   "Bohman",           0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BOHMAN} ,  0, 0, FLAGS, "win_func" },
    { "overlap",  "set window overlap", OFFSET(overlap), AV_OPT_TYPE_FLOAT, {.dbl=1.}, 0., 1., FLAGS },
    { "averaging", "set time averaging", OFFSET(avg), AV_OPT_TYPE_INT, {.i64=1}, 0, INT32_MAX, FLAGS },
    { "colors", "set channels colors", OFFSET(colors), AV_OPT_TYPE_STRING, {.str = "red|green|blue|yellow|orange|lime|pink|magenta|brown" }, 0, 0, FLAGS },
    { "cmode", "set channel mode", OFFSET(cmode), AV_OPT_TYPE_INT, {.i64=COMBINED}, 0, NB_CMODES-1, FLAGS, "cmode" },
        { "combined", "show all channels in same window",  0, AV_OPT_TYPE_CONST, {.i64=COMBINED}, 0, 0, FLAGS, "cmode" },
        { "separate", "show each channel in own window",   0, AV_OPT_TYPE_CONST, {.i64=SEPARATE}, 0, 0, FLAGS, "cmode" },
    { "minamp",  "set minimum amplitude", OFFSET(minamp), AV_OPT_TYPE_FLOAT, {.dbl=1e-6}, FLT_MIN, 1e-6, FLAGS },
    { NULL }
};

AVFILTER_DEFINE_CLASS(showfreqs);

static int query_formats(AVFilterContext *ctx)
{
    AVFilterFormats *formats = NULL;
    AVFilterChannelLayouts *layouts = NULL;
    AVFilterLink *inlink = ctx->inputs[0];
    AVFilterLink *outlink = ctx->outputs[0];
    static const enum AVSampleFormat sample_fmts[] = { AV_SAMPLE_FMT_FLTP, AV_SAMPLE_FMT_NONE };
    static const enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_RGBA, AV_PIX_FMT_NONE };
    int ret;

    /* set input audio formats */
    formats = ff_make_format_list(sample_fmts);
    if ((ret = ff_formats_ref(formats, &inlink->out_formats)) < 0)
        return ret;

    layouts = ff_all_channel_layouts();
    if ((ret = ff_channel_layouts_ref(layouts, &inlink->out_channel_layouts)) < 0)
        return ret;

    formats = ff_all_samplerates();
    if ((ret = ff_formats_ref(formats, &inlink->out_samplerates)) < 0)
        return ret;

    /* set output video format */
    formats = ff_make_format_list(pix_fmts);
    if ((ret = ff_formats_ref(formats, &outlink->in_formats)) < 0)
        return ret;

    return 0;
}

static av_cold int init(AVFilterContext *ctx)
{
    ShowFreqsContext *s = ctx->priv;

    s->pts = AV_NOPTS_VALUE;

    return 0;
}

static int config_output(AVFilterLink *outlink)
{
    AVFilterContext *ctx = outlink->src;
    AVFilterLink *inlink = ctx->inputs[0];
    ShowFreqsContext *s = ctx->priv;
    float overlap;
    int i;

    s->nb_freq = 1 << (s->fft_bits - 1);
    s->win_size = s->nb_freq << 1;
    av_audio_fifo_free(s->fifo);
    av_fft_end(s->fft);
    s->fft = av_fft_init(s->fft_bits, 0);
    if (!s->fft) {
        av_log(ctx, AV_LOG_ERROR, "Unable to create FFT context. "
               "The window size might be too high.\n");
        return AVERROR(ENOMEM);
    }

    /* FFT buffers: x2 for each (display) channel buffer.
     * Note: we use free and malloc instead of a realloc-like function to
     * make sure the buffer is aligned in memory for the FFT functions. */
    for (i = 0; i < s->nb_channels; i++) {
        av_freep(&s->fft_data[i]);
        av_freep(&s->avg_data[i]);
    }
    av_freep(&s->fft_data);
    av_freep(&s->avg_data);
    s->nb_channels = inlink->channels;

    s->fft_data = av_calloc(s->nb_channels, sizeof(*s->fft_data));
    if (!s->fft_data)
        return AVERROR(ENOMEM);
    s->avg_data = av_calloc(s->nb_channels, sizeof(*s->avg_data));
    if (!s->fft_data)
        return AVERROR(ENOMEM);
    for (i = 0; i < s->nb_channels; i++) {
        s->fft_data[i] = av_calloc(s->win_size, sizeof(**s->fft_data));
        s->avg_data[i] = av_calloc(s->nb_freq, sizeof(**s->avg_data));
        if (!s->fft_data[i] || !s->avg_data[i])
            return AVERROR(ENOMEM);
    }

    /* pre-calc windowing function */
    s->window_func_lut = av_realloc_f(s->window_func_lut, s->win_size,
                                      sizeof(*s->window_func_lut));
    if (!s->window_func_lut)
        return AVERROR(ENOMEM);
    generate_window_func(s->window_func_lut, s->win_size, s->win_func, &overlap);
    if (s->overlap == 1.)
        s->overlap = overlap;
    s->hop_size = (1. - s->overlap) * s->win_size;
    if (s->hop_size < 1) {
        av_log(ctx, AV_LOG_ERROR, "overlap %f too big\n", s->overlap);
        return AVERROR(EINVAL);
    }

    for (s->scale = 0, i = 0; i < s->win_size; i++) {
        s->scale += s->window_func_lut[i] * s->window_func_lut[i];
    }

    outlink->frame_rate = av_make_q(inlink->sample_rate, s->win_size * (1.-s->overlap));
    outlink->sample_aspect_ratio = (AVRational){1,1};
    outlink->w = s->w;
    outlink->h = s->h;

    s->fifo = av_audio_fifo_alloc(inlink->format, inlink->channels, s->win_size);
    if (!s->fifo)
        return AVERROR(ENOMEM);
    return 0;
}

static inline void draw_dot(AVFrame *out, int x, int y, uint8_t fg[4])
{

    uint32_t color = AV_RL32(out->data[0] + y * out->linesize[0] + x * 4);

    if ((color & 0xffffff) != 0)
        AV_WL32(out->data[0] + y * out->linesize[0] + x * 4, AV_RL32(fg) | color);
    else
        AV_WL32(out->data[0] + y * out->linesize[0] + x * 4, AV_RL32(fg));
}

static int get_sx(ShowFreqsContext *s, int f)
{
    switch (s->fscale) {
    case FS_LINEAR:
        return (s->w/(float)s->nb_freq)*f;
    case FS_LOG:
        return s->w-pow(s->w, (s->nb_freq-f-1)/(s->nb_freq-1.));
    case FS_RLOG:
        return pow(s->w, f/(s->nb_freq-1.));
    }

    return 0;
}

static float get_bsize(ShowFreqsContext *s, int f)
{
    switch (s->fscale) {
    case FS_LINEAR:
        return s->w/(float)s->nb_freq;
    case FS_LOG:
        return pow(s->w, (s->nb_freq-f-1)/(s->nb_freq-1.))-
               pow(s->w, (s->nb_freq-f-2)/(s->nb_freq-1.));
    case FS_RLOG:
        return pow(s->w, (f+1)/(s->nb_freq-1.))-
               pow(s->w,  f   /(s->nb_freq-1.));
    }

    return 1.;
}

static inline void plot_freq(ShowFreqsContext *s, int ch,
                             double a, int f, uint8_t fg[4], int *prev_y,
                             AVFrame *out, AVFilterLink *outlink)
{
    const int w = s->w;
    const float min = s->minamp;
    const float avg = s->avg_data[ch][f];
    const float bsize = get_bsize(s, f);
    const int sx = get_sx(s, f);
    int end = outlink->h;
    int x, y, i;

    switch(s->ascale) {
    case AS_SQRT:
        a = 1.0 - sqrt(a);
        break;
    case AS_CBRT:
        a = 1.0 - cbrt(a);
        break;
    case AS_LOG:
        a = log(av_clipd(a, min, 1)) / log(min);
        break;
    case AS_LINEAR:
        a = 1.0 - a;
        break;
    }

    switch (s->cmode) {
    case COMBINED:
        y = a * outlink->h - 1;
        break;
    case SEPARATE:
        end = (outlink->h / s->nb_channels) * (ch + 1);
        y = (outlink->h / s->nb_channels) * ch + a * (outlink->h / s->nb_channels) - 1;
        break;
    default:
        av_assert0(0);
    }
    if (y < 0)
        return;

    switch (s->avg) {
    case 0:
        y = s->avg_data[ch][f] = !outlink->frame_count_in ? y : FFMIN(avg, y);
        break;
    case 1:
        break;
    default:
        s->avg_data[ch][f] = avg + y * (y - avg) / (FFMIN(outlink->frame_count_in + 1, s->avg) * y);
        y = s->avg_data[ch][f];
        break;
    }

    switch(s->mode) {
    case LINE:
        if (*prev_y == -1) {
            *prev_y = y;
        }
        if (y <= *prev_y) {
            for (x = sx + 1; x < sx + bsize && x < w; x++)
                draw_dot(out, x, y, fg);
            for (i = y; i <= *prev_y; i++)
                draw_dot(out, sx, i, fg);
        } else {
            for (i = *prev_y; i <= y; i++)
                draw_dot(out, sx, i, fg);
            for (x = sx + 1; x < sx + bsize && x < w; x++)
                draw_dot(out, x, i - 1, fg);
        }
        *prev_y = y;
        break;
    case BAR:
        for (x = sx; x < sx + bsize && x < w; x++)
            for (i = y; i < end; i++)
                draw_dot(out, x, i, fg);
        break;
    case DOT:
        for (x = sx; x < sx + bsize && x < w; x++)
            draw_dot(out, x, y, fg);
        break;
    }
}

static int plot_freqs(AVFilterLink *inlink, AVFrame *in)
{
    AVFilterContext *ctx = inlink->dst;
    AVFilterLink *outlink = ctx->outputs[0];
    ShowFreqsContext *s = ctx->priv;
    const int win_size = s->win_size;
    char *colors, *color, *saveptr = NULL;
    AVFrame *out;
    int ch, n;

    out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
    if (!out)
        return AVERROR(ENOMEM);

    for (n = 0; n < outlink->h; n++)
        memset(out->data[0] + out->linesize[0] * n, 0, outlink->w * 4);

    /* fill FFT input with the number of samples available */
    for (ch = 0; ch < s->nb_channels; ch++) {
        const float *p = (float *)in->extended_data[ch];

        for (n = 0; n < in->nb_samples; n++) {
            s->fft_data[ch][n].re = p[n] * s->window_func_lut[n];
            s->fft_data[ch][n].im = 0;
        }
        for (; n < win_size; n++) {
            s->fft_data[ch][n].re = 0;
            s->fft_data[ch][n].im = 0;
        }
    }

    /* run FFT on each samples set */
    for (ch = 0; ch < s->nb_channels; ch++) {
        av_fft_permute(s->fft, s->fft_data[ch]);
        av_fft_calc(s->fft, s->fft_data[ch]);
    }

#define RE(x, ch) s->fft_data[ch][x].re
#define IM(x, ch) s->fft_data[ch][x].im
#define M(a, b) (sqrt((a) * (a) + (b) * (b)))

    colors = av_strdup(s->colors);
    if (!colors) {
        av_frame_free(&out);
        return AVERROR(ENOMEM);
    }

    for (ch = 0; ch < s->nb_channels; ch++) {
        uint8_t fg[4] = { 0xff, 0xff, 0xff, 0xff };
        int prev_y = -1, f;
        double a;

        color = av_strtok(ch == 0 ? colors : NULL, " |", &saveptr);
        if (color)
            av_parse_color(fg, color, -1, ctx);

        a = av_clipd(M(RE(0, ch), 0) / s->scale, 0, 1);
        plot_freq(s, ch, a, 0, fg, &prev_y, out, outlink);

        for (f = 1; f < s->nb_freq; f++) {
            a = av_clipd(M(RE(f, ch), IM(f, ch)) / s->scale, 0, 1);

            plot_freq(s, ch, a, f, fg, &prev_y, out, outlink);
        }
    }

    av_free(colors);
    out->pts = in->pts;
    out->sample_aspect_ratio = (AVRational){1,1};
    return ff_filter_frame(outlink, out);
}

static int filter_frame(AVFilterLink *inlink, AVFrame *in)
{
    AVFilterContext *ctx = inlink->dst;
    ShowFreqsContext *s = ctx->priv;
    AVFrame *fin = NULL;
    int consumed = 0;
    int ret = 0;

    if (s->pts == AV_NOPTS_VALUE)
        s->pts = in->pts - av_audio_fifo_size(s->fifo);

    av_audio_fifo_write(s->fifo, (void **)in->extended_data, in->nb_samples);
    while (av_audio_fifo_size(s->fifo) >= s->win_size) {
        fin = ff_get_audio_buffer(inlink, s->win_size);
        if (!fin) {
            ret = AVERROR(ENOMEM);
            goto fail;
        }

        fin->pts = s->pts + consumed;
        consumed += s->hop_size;
        ret = av_audio_fifo_peek(s->fifo, (void **)fin->extended_data, s->win_size);
        if (ret < 0)
            goto fail;

        ret = plot_freqs(inlink, fin);
        av_frame_free(&fin);
        av_audio_fifo_drain(s->fifo, s->hop_size);
        if (ret < 0)
            goto fail;
    }

fail:
    s->pts = AV_NOPTS_VALUE;
    av_frame_free(&fin);
    av_frame_free(&in);
    return ret;
}

static av_cold void uninit(AVFilterContext *ctx)
{
    ShowFreqsContext *s = ctx->priv;
    int i;

    av_fft_end(s->fft);
    for (i = 0; i < s->nb_channels; i++) {
        if (s->fft_data)
            av_freep(&s->fft_data[i]);
        if (s->avg_data)
            av_freep(&s->avg_data[i]);
    }
    av_freep(&s->fft_data);
    av_freep(&s->avg_data);
    av_freep(&s->window_func_lut);
    av_audio_fifo_free(s->fifo);
}

static const AVFilterPad showfreqs_inputs[] = {
    {
        .name         = "default",
        .type         = AVMEDIA_TYPE_AUDIO,
        .filter_frame = filter_frame,
    },
    { NULL }
};

static const AVFilterPad showfreqs_outputs[] = {
    {
        .name          = "default",
        .type          = AVMEDIA_TYPE_VIDEO,
        .config_props  = config_output,
    },
    { NULL }
};

AVFilter ff_avf_showfreqs = {
    .name          = "showfreqs",
    .description   = NULL_IF_CONFIG_SMALL("Convert input audio to a frequencies video output."),
    .init          = init,
    .uninit        = uninit,
    .query_formats = query_formats,
    .priv_size     = sizeof(ShowFreqsContext),
    .inputs        = showfreqs_inputs,
    .outputs       = showfreqs_outputs,
    .priv_class    = &showfreqs_class,
};