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

Paul B Mahol onemda at gmail.com
Thu Sep 24 17:24:39 CEST 2015


On 9/24/15, Kyle Swanson <k at ylo.ph> wrote:
> Sorry, I meant to type (1.0 / s->freq). This is one wavelength.


I inspected what filter produces with constant 0.5 mono input and
found it is repeating after each sample_rate number of samples.

Please do not top post.

>
> On Thu, Sep 24, 2015 at 9:29 AM, Kyle Swanson <k at ylo.ph> wrote:
>>>  s->table = av_malloc_array(inlink->sample_rate, sizeof(*s->table));
>>
>>
>> Just wondering. Is there a reason that the size of s->table is
>> (inlink->sample_rate)  and not (1.0 / inlink->sample_rate) ?
>>
>> Thanks!
>> Kyle
>>
>> On Wed, Sep 23, 2015 at 6:16 PM, Kyle Swanson <k at ylo.ph> wrote:
>>> 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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