avfilter/af_biquads: make commands work reliably within biquad filter

Previously changing single coefficient would give unexpected results.

libavfilter/af_biquads.c

@@ -127,6 +127,9 @@ typedef struct BiquadsContext {
     double a0, a1, a2;
     double b0, b1, b2;
 
+    double oa0, oa1, oa2;
+    double ob0, ob1, ob2;
+
     ChanCache *cache;
     int block_align;
 
@@ -480,6 +483,12 @@ static int config_filter(AVFilterLink *outlink, int reset)
 
     switch (s->filter_type) {
     case biquad:
+        s->a0 = s->oa0;
+        s->a1 = s->oa1;
+        s->a2 = s->oa2;
+        s->b0 = s->ob0;
+        s->b1 = s->ob1;
+        s->b2 = s->ob2;
         break;
     case equalizer:
         s->a0 =   1 + alpha / A;
@@ -1154,12 +1163,12 @@ DEFINE_BIQUAD_FILTER(highshelf, "Apply a high shelf filter.");
 #endif  /* CONFIG_HIGHSHELF_FILTER */
 #if CONFIG_BIQUAD_FILTER
 static const AVOption biquad_options[] = {
-    {"a0", NULL, OFFSET(a0), AV_OPT_TYPE_DOUBLE, {.dbl=1}, INT32_MIN, INT32_MAX, FLAGS},
-    {"a1", NULL, OFFSET(a1), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
-    {"a2", NULL, OFFSET(a2), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
-    {"b0", NULL, OFFSET(b0), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
-    {"b1", NULL, OFFSET(b1), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
-    {"b2", NULL, OFFSET(b2), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
+    {"a0", NULL, OFFSET(oa0), AV_OPT_TYPE_DOUBLE, {.dbl=1}, INT32_MIN, INT32_MAX, FLAGS},
+    {"a1", NULL, OFFSET(oa1), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
+    {"a2", NULL, OFFSET(oa2), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
+    {"b0", NULL, OFFSET(ob0), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
+    {"b1", NULL, OFFSET(ob1), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
+    {"b2", NULL, OFFSET(ob2), AV_OPT_TYPE_DOUBLE, {.dbl=0}, INT32_MIN, INT32_MAX, FLAGS},
     {"mix", "set mix", OFFSET(mix), AV_OPT_TYPE_DOUBLE, {.dbl=1}, 0, 1, FLAGS},
     {"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},