avfilter/af_astats: measure dynamic range

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

doc/filters.texi

@@ -1623,6 +1623,7 @@ Crest_factor
 Flat_factor
 Peak_count
 Bit_depth
+Dynamic_range
 
 and for Overall:
 DC_offset
@@ -1697,6 +1698,9 @@ Number of occasions (not the number of samples) that the signal attained either
 
 @item Bit depth
 Overall bit depth of audio. Number of bits used for each sample.
+
+@item Dynamic range
+Measured dynamic range of audio in dB.
 @end table
 
 @section atempo

libavfilter/af_astats.c

@@ -28,6 +28,7 @@
 
 typedef struct ChannelStats {
     double last;
+    double min_non_zero;
     double sigma_x, sigma_x2;
     double avg_sigma_x2, min_sigma_x2, max_sigma_x2;
     double min, max;
@@ -110,6 +111,7 @@ static void reset_stats(AudioStatsContext *s)
 
         p->min = p->nmin = p->min_sigma_x2 = DBL_MAX;
         p->max = p->nmax = p->max_sigma_x2 = DBL_MIN;
+        p->min_non_zero = DBL_MAX;
         p->min_diff = DBL_MAX;
         p->max_diff = DBL_MIN;
         p->sigma_x = 0;
@@ -178,6 +180,9 @@ static inline void update_stat(AudioStatsContext *s, ChannelStats *p, double d,
         p->min_runs += p->min_run * p->min_run;
     }
 
+    if (d != 0 && FFABS(d) < p->min_non_zero)
+        p->min_non_zero = FFABS(d);
+
     if (d > p->max) {
         p->max = d;
         p->nmax = nd;
@@ -286,6 +291,7 @@ static void set_metadata(AudioStatsContext *s, AVDictionary **metadata)
         bit_depth(s, p->mask, p->imask, &depth);
         set_meta(metadata, c + 1, "Bit_depth", "%f", depth.num);
         set_meta(metadata, c + 1, "Bit_depth2", "%f", depth.den);
+        set_meta(metadata, c + 1, "Dynamic_range", "%f", LINEAR_TO_DB(2 * FFMAX(FFABS(p->min), FFABS(p->max))/ p->min_non_zero));
     }
 
     set_meta(metadata, 0, "Overall.DC_offset", "%f", max_sigma_x / (nb_samples / s->nb_channels));
@@ -479,6 +485,7 @@ static void print_stats(AVFilterContext *ctx)
         av_log(ctx, AV_LOG_INFO, "Peak count: %"PRId64"\n", p->min_count + p->max_count);
         bit_depth(s, p->mask, p->imask, &depth);
         av_log(ctx, AV_LOG_INFO, "Bit depth: %u/%u\n", depth.num, depth.den);
+        av_log(ctx, AV_LOG_INFO, "Dynamic range: %f\n", LINEAR_TO_DB(2 * FFMAX(FFABS(p->min), FFABS(p->max))/ p->min_non_zero));
     }
 
     av_log(ctx, AV_LOG_INFO, "Overall\n");