libavfilter/ebur128: introduce target range

This eases meeting the target level during live mixing.

Signed-off-by: Daniel Molkentin <daniel@molkentin.de>
Signed-off-by: Conrad Zelck <c.zelck@imail.de>

doc/filters.texi

@@ -19284,6 +19284,9 @@ short-term loudness (3 seconds of analysis), and the gauge on the right is for
 the momentary loudness (400 milliseconds), but can optionally be configured
 to instead display short-term loudness (see @var{gauge}).
+The green area marks a  +/- 1LU target range around the target loudness
+(-23LUFS by default, unless modified through @var{target}).
+
 More information about the Loudness Recommendation EBU R128 on
 @url{http://tech.ebu.ch/loudness}.

libavfilter/f_ebur128.c

@@ -114,6 +114,8 @@ typedef struct EBUR128Context {
     int meter;                      ///< select a EBU mode between +9 and +18
     int scale_range;                ///< the range of LU values according to the meter
     int y_zero_lu;                  ///< the y value (pixel position) for 0 LU
+    int y_opt_max;                  ///< the y value (pixel position) for 1 LU
+    int y_opt_min;                  ///< the y value (pixel position) for -1 LU
     int *y_line_ref;                ///< y reference values for drawing the LU lines in the graph and the gauge
 
     /* audio */
@@ -188,22 +190,31 @@ static const AVOption ebur128_options[] = {
 AVFILTER_DEFINE_CLASS(ebur128);
 
 static const uint8_t graph_colors[] = {
-    0xdd, 0x66, 0x66,   // value above 0LU non reached
-    0x66, 0x66, 0xdd,   // value below 0LU non reached
-    0x96, 0x33, 0x33,   // value above 0LU reached
-    0x33, 0x33, 0x96,   // value below 0LU reached
-    0xdd, 0x96, 0x96,   // value above 0LU line non reached
-    0x96, 0x96, 0xdd,   // value below 0LU line non reached
-    0xdd, 0x33, 0x33,   // value above 0LU line reached
-    0x33, 0x33, 0xdd,   // value below 0LU line reached
+    0xdd, 0x66, 0x66,   // value above 1LU non reached below -1LU (impossible)
+    0x66, 0x66, 0xdd,   // value below 1LU non reached below -1LU
+    0x96, 0x33, 0x33,   // value above 1LU reached below -1LU (impossible)
+    0x33, 0x33, 0x96,   // value below 1LU reached below -1LU
+    0xdd, 0x96, 0x96,   // value above 1LU line non reached below -1LU (impossible)
+    0x96, 0x96, 0xdd,   // value below 1LU line non reached below -1LU
+    0xdd, 0x33, 0x33,   // value above 1LU line reached below -1LU (impossible)
+    0x33, 0x33, 0xdd,   // value below 1LU line reached below -1LU
+    0xdd, 0x66, 0x66,   // value above 1LU non reached above -1LU
+    0x66, 0xdd, 0x66,   // value below 1LU non reached above -1LU
+    0x96, 0x33, 0x33,   // value above 1LU reached above -1LU
+    0x33, 0x96, 0x33,   // value below 1LU reached above -1LU
+    0xdd, 0x96, 0x96,   // value above 1LU line non reached above -1LU
+    0x96, 0xdd, 0x96,   // value below 1LU line non reached above -1LU
+    0xdd, 0x33, 0x33,   // value above 1LU line reached above -1LU
+    0x33, 0xdd, 0x33,   // value below 1LU line reached above -1LU
 };
 
 static const uint8_t *get_graph_color(const EBUR128Context *ebur128, int v, int y)
 {
-    const int below0  = y > ebur128->y_zero_lu;
+    const int above_opt_max = y > ebur128->y_opt_max;
+    const int below_opt_min = y < ebur128->y_opt_min;
     const int reached = y >= v;
     const int line    = ebur128->y_line_ref[y] || y == ebur128->y_zero_lu;
-    const int colorid = 4*line + 2*reached + below0;
+    const int colorid = 8*below_opt_min+ 4*line + 2*reached + above_opt_max;
     return graph_colors + 3*colorid;
 }
 
@@ -337,6 +348,8 @@ static int config_video_output(AVFilterLink *outlink)
 
     /* draw graph */
     ebur128->y_zero_lu = lu_to_y(ebur128, 0);
+    ebur128->y_opt_max = lu_to_y(ebur128, 1);
+    ebur128->y_opt_min = lu_to_y(ebur128, -1);
     p = outpicref->data[0] + ebur128->graph.y * outpicref->linesize[0]
                            + ebur128->graph.x * 3;
     for (y = 0; y < ebur128->graph.h; y++) {