avfilter/af_biquads: add new normalize/n option

doc/filters.texi

@@ -1547,6 +1547,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Commands
@@ -2568,6 +2572,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Commands
@@ -2627,6 +2635,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Commands
@@ -2693,6 +2705,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Commands
@@ -2744,6 +2760,13 @@ Syntax for the command is : "@var{value}"
 @item mix, m
 How much to use filtered signal in output. Default is 1.
 Range is between 0 and 1.
+
+@item channels, c
+Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @section bs2b
@@ -3439,6 +3462,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Examples
@@ -3908,6 +3935,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Commands
@@ -4224,6 +4255,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Examples
@@ -5332,6 +5367,10 @@ Range is between 0 and 1.
 
 @item channels, c
 Specify which channels to filter, by default all available are filtered.
+
+@item normalize, n
+Normalize biquad coefficients, by default is disabled.
+Enabling it will normalize magnitude response at DC to 0dB.
 @end table
 
 @subsection Commands

libavfilter/af_biquads.c

@@ -112,6 +112,7 @@ typedef struct BiquadsContext {
     double width;
     double mix;
     uint64_t channels;
+    int normalize;
 
     double a0, a1, a2;
     double b0, b1, b2;
@@ -408,6 +409,14 @@ static int config_filter(AVFilterLink *outlink, int reset)
     s->b2 /= s->a0;
     s->a0 /= s->a0;
 
+    if (s->normalize && fabs(s->b0 + s->b1 + s->b2) > 1e-6) {
+        double factor = (s->a0 + s->a1 + s->a2) / (s->b0 + s->b1 + s->b2);
+
+        s->b0 *= factor;
+        s->b1 *= factor;
+        s->b2 *= factor;
+    }
+
     s->cache = av_realloc_f(s->cache, sizeof(ChanCache), inlink->channels);
     if (!s->cache)
         return AVERROR(ENOMEM);
@@ -585,6 +594,8 @@ static const AVOption equalizer_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -609,6 +620,8 @@ static const AVOption bass_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -633,6 +646,8 @@ static const AVOption treble_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -656,6 +671,8 @@ static const AVOption bandpass_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -678,6 +695,8 @@ static const AVOption bandreject_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -702,6 +721,8 @@ static const AVOption lowpass_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -726,6 +747,8 @@ static const AVOption highpass_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -748,6 +771,8 @@ static const AVOption allpass_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -772,6 +797,8 @@ static const AVOption lowshelf_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -796,6 +823,8 @@ static const AVOption highshelf_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };
 
@@ -813,6 +842,8 @@ static const AVOption biquad_options[] = {
     {"m",   "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"channels", "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
     {"c",        "set channels to filter", OFFSET(channels), AV_OPT_TYPE_CHANNEL_LAYOUT, {.i64=-1}, INT64_MIN, INT64_MAX, FLAGS},
+    {"normalize", "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
+    {"n",         "normalize coefficients", OFFSET(normalize), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {NULL}
 };