avfilter/af_afir: rework FIR gain measurement

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/af_afir.c

@@ -105,7 +105,7 @@ static int fir_channel(AVFilterContext *ctx, void *arg, int ch, int nb_jobs)
 
     if (out) {
         float *ptr = (float *)out->extended_data[ch];
-        s->fdsp->vector_fmul_scalar(ptr, dst, s->gain * s->wet_gain, FFALIGN(out->nb_samples, 4));
+        s->fdsp->vector_fmul_scalar(ptr, dst, s->wet_gain, FFALIGN(out->nb_samples, 4));
         emms_c();
     }
 
@@ -166,7 +166,6 @@ static int convert_coeffs(AVFilterContext *ctx)
 {
     AudioFIRContext *s = ctx->priv;
     int i, ch, n, N;
-    float power = 0;
 
     s->nb_taps = av_audio_fifo_size(s->fifo[1]);
     if (s->nb_taps <= 0)
@@ -217,13 +216,29 @@ static int convert_coeffs(AVFilterContext *ctx)
 
     av_audio_fifo_read(s->fifo[1], (void **)s->in[1]->extended_data, s->nb_taps);
 
+    if (s->again) {
+        float power = 0;
+
+        for (ch = 0; ch < ctx->inputs[1]->channels; ch++) {
+            float *time = (float *)s->in[1]->extended_data[!s->one2many * ch];
+
+            for (i = 0; i < s->nb_taps; i++)
+                power += FFABS(time[i]);
+        }
+
+        s->gain = sqrtf(1.f / (ctx->inputs[1]->channels * power)) / (sqrtf(ctx->inputs[1]->channels));
+        for (ch = 0; ch < ctx->inputs[1]->channels; ch++) {
+            float *time = (float *)s->in[1]->extended_data[!s->one2many * ch];
+
+            s->fdsp->vector_fmul_scalar(time, time, s->gain, FFALIGN(s->nb_taps, 4));
+        }
+    }
+
     for (ch = 0; ch < ctx->inputs[1]->channels; ch++) {
         float *time = (float *)s->in[1]->extended_data[!s->one2many * ch];
         float *block = s->block[ch];
         FFTComplex *coeff = s->coeff[ch];
 
-        power += s->fdsp->scalarproduct_float(time, time, s->nb_taps);
-
         for (i = FFMAX(1, s->length * s->nb_taps); i < s->nb_taps; i++)
             time[i] = 0;
 
@@ -252,7 +267,6 @@ static int convert_coeffs(AVFilterContext *ctx)
     }
 
     av_frame_free(&s->in[1]);
-    s->gain = s->again ? 1.f / sqrtf(power / ctx->inputs[1]->channels) : 1.f;
     av_log(ctx, AV_LOG_DEBUG, "nb_taps: %d\n", s->nb_taps);
     av_log(ctx, AV_LOG_DEBUG, "nb_partitions: %d\n", s->nb_partitions);
     av_log(ctx, AV_LOG_DEBUG, "partition size: %d\n", s->part_size);