On Mon, 30 Nov 2020, Paul B Mahol wrote:

Signed-off-by: Paul B Mahol <one...@gmail.com>
---
doc/filters.texi           | 25 +++++++++++
libavfilter/Makefile       |  1 +
libavfilter/af_asupercut.c | 89 ++++++++++++++++++++++++++++++--------
libavfilter/allfilters.c   |  1 +
4 files changed, 97 insertions(+), 19 deletions(-)

diff --git a/doc/filters.texi b/doc/filters.texi
index 06ed28f3f9..348cdae4e9 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -2636,6 +2636,28 @@ Default value is 20.

This filter supports the all above options as @ref{commands}.

+@section asubcut
+Cut subwoofer frequencies.

Please explain in the documentation how is this different from a simple highpass filter, and when it is preferable to use this and when to use highpass.

Thanks,
Marton

+
+The filter accepts the following options:
+
+@table @option
+@item cutoff
+Set cutoff frequency in Hertz. Allowed range is 2 to 200.
+Default value is 20.
+
+@item order
+Set filter order. Available values are from 3 to 20.
+Default value is 10.
+
+@item level
+Set input gain level. Allowed range is from 0 to 1. Default value is 1.
+@end table
+
+@subsection Commands
+
+This filter supports the all above options as @ref{commands}.
+
@section asupercut
Cut super frequencies.

@@ -2649,6 +2671,9 @@ Default value is 20000.
@item order
Set filter order. Available values are from 3 to 20.
Default value is 10.
+
+@item level
+Set input gain level. Allowed range is from 0 to 1. Default value is 1.
@end table

@subsection Commands
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index cff9402989..03998dc064 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -90,6 +90,7 @@ OBJS-$(CONFIG_ASR_FILTER)                    += af_asr.o
OBJS-$(CONFIG_ASTATS_FILTER)                 += af_astats.o
OBJS-$(CONFIG_ASTREAMSELECT_FILTER)          += f_streamselect.o framesync.o
OBJS-$(CONFIG_ASUBBOOST_FILTER)              += af_asubboost.o
+OBJS-$(CONFIG_ASUBCUT_FILTER)                += af_asupercut.o
OBJS-$(CONFIG_ASUPERCUT_FILTER)              += af_asupercut.o
OBJS-$(CONFIG_ATEMPO_FILTER)                 += af_atempo.o
OBJS-$(CONFIG_ATRIM_FILTER)                  += trim.o
diff --git a/libavfilter/af_asupercut.c b/libavfilter/af_asupercut.c
index ef241405d8..6d0a2b79a9 100644
--- a/libavfilter/af_asupercut.c
+++ b/libavfilter/af_asupercut.c
@@ -32,6 +32,7 @@ typedef struct ASuperCutContext {
    const AVClass *class;

    double cutoff;
+    double level;
    int order;

    int filter_count;
@@ -95,27 +96,52 @@ static int get_coeffs(AVFilterContext *ctx)
    s->filter_count = s->order / 2 + (s->order & 1);
    calc_q_factors(s->order, q);

-    if (s->order & 1) {
-        BiquadCoeffs *coeffs = &s->coeffs[0];
-        double omega = 2. * tan(M_PI * w0);
+    if (!strcmp(ctx->filter->name, "asubcut")) {
+        if (s->order & 1) {
+            BiquadCoeffs *coeffs = &s->coeffs[0];
+            double omega = 2. * tan(M_PI * w0);

-        coeffs->b0 = omega / (2. + omega);
-        coeffs->b1 = coeffs->b0;
-        coeffs->b2 = 0.;
-        coeffs->a1 = -(omega - 2.) / (2. + omega);
-        coeffs->a2 = 0.;
-    }
+            coeffs->b0 = 2. / (2. + omega);
+            coeffs->b1 = -coeffs->b0;
+            coeffs->b2 = 0.;
+            coeffs->a1 = -(omega - 2.) / (2. + omega);
+            coeffs->a2 = 0.;
+        }
+
+        for (int b = (s->order & 1); b < s->filter_count; b++) {
+            BiquadCoeffs *coeffs = &s->coeffs[b];
+            const int idx = b - (s->order & 1);
+            double norm = 1.0 / (1.0 + K / q[idx] + K * K);

-    for (int b = (s->order & 1); b < s->filter_count; b++) {
-        BiquadCoeffs *coeffs = &s->coeffs[b];
-        const int idx = b - (s->order & 1);
-        double norm = 1.0 / (1.0 + K / q[idx] + K * K);
+            coeffs->b0 = norm;
+            coeffs->b1 = -2.0 * coeffs->b0;
+            coeffs->b2 = coeffs->b0;
+            coeffs->a1 = -2.0 * (K * K - 1.0) * norm;
+            coeffs->a2 = -(1.0 - K / q[idx] + K * K) * norm;
+        }
+    } else {
+        if (s->order & 1) {
+            BiquadCoeffs *coeffs = &s->coeffs[0];
+            double omega = 2. * tan(M_PI * w0);
+
+            coeffs->b0 = omega / (2. + omega);
+            coeffs->b1 = coeffs->b0;
+            coeffs->b2 = 0.;
+            coeffs->a1 = -(omega - 2.) / (2. + omega);
+            coeffs->a2 = 0.;
+        }

-        coeffs->b0 = K * K * norm;
-        coeffs->b1 = 2.0 * coeffs->b0;
-        coeffs->b2 = coeffs->b0;
-        coeffs->a1 = -2.0 * (K * K - 1.0) * norm;
-        coeffs->a2 = -(1.0 - K / q[idx] + K * K) * norm;
+        for (int b = (s->order & 1); b < s->filter_count; b++) {
+            BiquadCoeffs *coeffs = &s->coeffs[b];
+            const int idx = b - (s->order & 1);
+            double norm = 1.0 / (1.0 + K / q[idx] + K * K);
+
+            coeffs->b0 = K * K * norm;
+            coeffs->b1 = 2.0 * coeffs->b0;
+            coeffs->b2 = coeffs->b0;
+            coeffs->a1 = -2.0 * (K * K - 1.0) * norm;
+            coeffs->a2 = -(1.0 - K / q[idx] + K * K) * norm;
+        }
    }

    return 0;
@@ -135,6 +161,7 @@ static int filter_channels_## name(AVFilterContext *ctx, 
void *arg, \
    AVFrame *in = td->in;                                           \
    const int start = (in->channels * jobnr) / nb_jobs;             \
    const int end = (in->channels * (jobnr+1)) / nb_jobs;           \
+    const double level = s->level;                                  \
                                                                    \
    for (int ch = start; ch < end; ch++) {                          \
        const type *src = (const type *)in->extended_data[ch];      \
@@ -150,7 +177,7 @@ static int filter_channels_## name(AVFilterContext *ctx, 
void *arg, \
            type *w = ((type *)s->w->extended_data[ch]) + b * 2;    \
                                                                    \
            for (int n = 0; n < in->nb_samples; n++) {              \
-                type sin = b ? dst[n] : src[n];                     \
+                type sin = b ? dst[n] : src[n] * level;             \
                type sout = sin * b0 + w[0];                        \
                                                                    \
                w[0] = b1 * sin + w[1] + a1 * sout;                 \
@@ -240,6 +267,7 @@ static av_cold void uninit(AVFilterContext *ctx)
static const AVOption asupercut_options[] = {
    { "cutoff", "set cutoff frequency", OFFSET(cutoff), AV_OPT_TYPE_DOUBLE, 
{.dbl=20000}, 20000, 192000, FLAGS },
    { "order",  "set filter order",     OFFSET(order),  AV_OPT_TYPE_INT,    
{.i64=10},        3,     20, FLAGS },
+    { "level",  "set input level",      OFFSET(level),  AV_OPT_TYPE_DOUBLE, 
{.dbl=1.},        0.,    1., FLAGS },
    { NULL }
};

@@ -276,3 +304,26 @@ AVFilter ff_af_asupercut = {
    .flags           = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC |
                       AVFILTER_FLAG_SLICE_THREADS,
};
+
+static const AVOption asubcut_options[] = {
+    { "cutoff", "set cutoff frequency", OFFSET(cutoff), AV_OPT_TYPE_DOUBLE, 
{.dbl=20},  2, 200, FLAGS },
+    { "order",  "set filter order",     OFFSET(order),  AV_OPT_TYPE_INT,    
{.i64=10},  3,  20, FLAGS },
+    { "level",  "set input level",      OFFSET(level),  AV_OPT_TYPE_DOUBLE, 
{.dbl=1.}, 0.,  1., FLAGS },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(asubcut);
+
+AVFilter ff_af_asubcut = {
+    .name            = "asubcut",
+    .description     = NULL_IF_CONFIG_SMALL("Cut subwoofer frequencies."),
+    .query_formats   = query_formats,
+    .priv_size       = sizeof(ASuperCutContext),
+    .priv_class      = &asubcut_class,
+    .uninit          = uninit,
+    .inputs          = inputs,
+    .outputs         = outputs,
+    .process_command = process_command,
+    .flags           = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC |
+                       AVFILTER_FLAG_SLICE_THREADS,
+};
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 83f434bc27..d0fb7bfe9d 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -83,6 +83,7 @@ extern AVFilter ff_af_asr;
extern AVFilter ff_af_astats;
extern AVFilter ff_af_astreamselect;
extern AVFilter ff_af_asubboost;
+extern AVFilter ff_af_asubcut;
extern AVFilter ff_af_asupercut;
extern AVFilter ff_af_atempo;
extern AVFilter ff_af_atrim;
--
2.17.1

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