[FFmpeg-devel] [PATCH] avfilter/af_tremolo: make it bit-exact with sox effect of same name

[Kyle Swanson]

Looks good. Thanks for the clean-up.

On Wed, Sep 23, 2015 at 4:22 PM, Paul B Mahol <onemda at gmail.com> wrote:
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  libavfilter/Makefile     |  2 +-
>  libavfilter/af_tremolo.c | 45 ++++++++++++++++++++++-----------------------
>  2 files changed, 23 insertions(+), 24 deletions(-)
>
> diff --git a/libavfilter/Makefile b/libavfilter/Makefile
> index 7054275..c70887e 100644
> --- a/libavfilter/Makefile
> +++ b/libavfilter/Makefile
> @@ -85,7 +85,7 @@ OBJS-$(CONFIG_SILENCEREMOVE_FILTER)          += af_silenceremove.o
>  OBJS-$(CONFIG_STEREOTOOLS_FILTER)            += af_stereotools.o
>  OBJS-$(CONFIG_STEREOWIDEN_FILTER)            += af_stereowiden.o
>  OBJS-$(CONFIG_TREBLE_FILTER)                 += af_biquads.o
> -OBJS-$(CONFIG_TREMOLO_FILTER)                += af_tremolo.o generate_wave_table.o
> +OBJS-$(CONFIG_TREMOLO_FILTER)                += af_tremolo.o
>  OBJS-$(CONFIG_VOLUME_FILTER)                 += af_volume.o
>  OBJS-$(CONFIG_VOLUMEDETECT_FILTER)           += af_volumedetect.o
>
> diff --git a/libavfilter/af_tremolo.c b/libavfilter/af_tremolo.c
> index 6335401..0ae7a7c 100644
> --- a/libavfilter/af_tremolo.c
> +++ b/libavfilter/af_tremolo.c
> @@ -22,15 +22,13 @@
>  #include "avfilter.h"
>  #include "internal.h"
>  #include "audio.h"
> -#include "generate_wave_table.h"
>
>  typedef struct TremoloContext {
>      const AVClass *class;
>      double freq;
>      double depth;
> -    double *wave_table;
> -    int wave_table_index;
> -    int sample_rate;
> +    double *table;
> +    int index;
>  } TremoloContext;
>
>  #define OFFSET(x) offsetof(TremoloContext, x)
> @@ -44,20 +42,11 @@ static const AVOption tremolo_options[] = {
>
>  AVFILTER_DEFINE_CLASS(tremolo);
>
> -static double trem_env(AVFilterContext *ctx)
> -{
> -    TremoloContext *s = ctx->priv;
> -    double env = s->wave_table[s->wave_table_index];
> -    s->wave_table_index++;
> -    if (s->wave_table_index >= s->sample_rate / s->freq)
> -        s->wave_table_index = 0;
> -    return 1.0 - (s->depth * env);
> -}
> -
>  static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>  {
>      AVFilterContext *ctx = inlink->dst;
>      AVFilterLink *outlink = ctx->outputs[0];
> +    TremoloContext *s = ctx->priv;
>      const double *src = (const double *)in->data[0];
>      const int channels = inlink->channels;
>      const int nb_samples = in->nb_samples;
> @@ -78,12 +67,13 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>      dst = (double *)out->data[0];
>
>      for (n = 0; n < nb_samples; n++) {
> -        const double env = trem_env(ctx);
> -
>          for (c = 0; c < channels; c++)
> -            dst[c] = src[c] * env;
> +            dst[c] = src[c] * s->table[s->index];
>          dst += channels;
>          src += channels;
> +        s->index++;
> +        if (s->index >= inlink->sample_rate)
> +            s->index = 0;
>      }
>
>      if (in != out)
> @@ -125,21 +115,30 @@ static int query_formats(AVFilterContext *ctx)
>  static av_cold void uninit(AVFilterContext *ctx)
>  {
>      TremoloContext *s = ctx->priv;
> -    av_freep(&s->wave_table);
> +    av_freep(&s->table);
>  }
>
>  static int config_input(AVFilterLink *inlink)
>  {
>      AVFilterContext *ctx = inlink->dst;
>      TremoloContext *s = ctx->priv;
> +    const double offset = 1. - s->depth / 2.;
> +    int i;
>
> -    s->sample_rate = inlink->sample_rate;
> -    s->wave_table = av_malloc_array(s->sample_rate / s->freq, sizeof(*s->wave_table));
> -    if (!s->wave_table)
> +    s->table = av_malloc_array(inlink->sample_rate, sizeof(*s->table));
> +    if (!s->table)
>          return AVERROR(ENOMEM);
>
> -    ff_generate_wave_table(WAVE_SIN, AV_SAMPLE_FMT_DBL, s->wave_table, s->sample_rate / s->freq, 0.0, 1.0, 0.0);
> -    s->wave_table_index = 0;
> +    for (i = 0; i < inlink->sample_rate; i++) {
> +        double env = s->freq * i / inlink->sample_rate;
> +
> +        env = sin(2 * M_PI * fmod(env + 0.25, 1.0));
> +
> +        s->table[i] = env * (1 - fabs(offset)) + offset;
> +    }
> +
> +    s->index = 0;
> +
>      return 0;
>  }
>
> --
> 1.9.1
>
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