@@ -12685,6 +12685,15 @@ stream for better peak accuracy. It logs a message for true-peak.

 This mode requires a build with @code{libswresample}.

 @end table

+@item dualmono

+Treat mono input files as "dual mono". If a mono file is intended for playback

+on a stereo system, its EBU R128 measurement will be perceptually incorrect.

+If set to @code{true}, this option will compensate for this effect.

+Multi-channel input files are not effected by this option.

+

+@item panlaw

+Set a specific pan law to be used for the measurement of dual mono files.

+This parameter is optional, and has a default value of -3.01dB.

 @end table

 @subsection Examples

@@ -139,6 +139,8 @@ typedef struct {

     /* misc */

     int loglevel;                   ///< log level for frame logging

     int metadata;                   ///< whether or not to inject loudness results in frames

+    int dual_mono;                  ///< whether or not to treat single channel input files as dual-mono

+    double pan_law;                 ///< pan law value used to calulate dual-mono measurements

 } EBUR128Context;

 enum {

@@ -163,6 +165,8 @@ static const AVOption ebur128_options[] = {

         { "none",   "disable any peak mode",   0, AV_OPT_TYPE_CONST, {.i64 = PEAK_MODE_NONE},          INT_MIN, INT_MAX, A|F, "mode" },

         { "sample", "enable peak-sample mode", 0, AV_OPT_TYPE_CONST, {.i64 = PEAK_MODE_SAMPLES_PEAKS}, INT_MIN, INT_MAX, A|F, "mode" },

         { "true",   "enable true-peak mode",   0, AV_OPT_TYPE_CONST, {.i64 = PEAK_MODE_TRUE_PEAKS},    INT_MIN, INT_MAX, A|F, "mode" },

+    { "dualmono", "treat mono input files as dual-mono", OFFSET(dual_mono), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, A|F },

+    { "panlaw", "set a specific pan law for dual-mono files", OFFSET(pan_law), AV_OPT_TYPE_DOUBLE, {.dbl = -3.01029995663978}, -10.0, 0.0, A|F },

     { NULL },

 };

@@ -661,6 +665,10 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)

                 }

                 if (nb_integrated)

                     ebur128->integrated_loudness = LOUDNESS(integrated_sum / nb_integrated);

+                    /* dual-mono correction */

+                    if (nb_channels == 1 && ebur128->dual_mono) {

+                        ebur128->integrated_loudness -= ebur128->pan_law;

+                    }

             }

             /* LRA */

@@ -707,6 +715,12 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)

                 }

             }

+            /* dual-mono correction */

+            if (nb_channels == 1 && ebur128->dual_mono) {

+                loudness_400 -= ebur128->pan_law;

+                loudness_3000 -= ebur128->pan_law;

+            }

+

 #define LOG_FMT "M:%6.1f S:%6.1f     I:%6.1f LUFS     LRA:%6.1f LU"

             /* push one video frame */

@@ -855,6 +869,14 @@ static av_cold void uninit(AVFilterContext *ctx)

     int i;

     EBUR128Context *ebur128 = ctx->priv;

+    /* dual-mono correction */

+    if (ebur128->nb_channels == 1 && ebur128->dual_mono) {

+        ebur128->i400.rel_threshold -= ebur128->pan_law;

+        ebur128->i3000.rel_threshold -= ebur128->pan_law;

+        ebur128->lra_low -= ebur128->pan_law;

+        ebur128->lra_high -= ebur128->pan_law;

+    }

+

     av_log(ctx, AV_LOG_INFO, "Summary:\n\n"

            "  Integrated loudness:\n"

            "    I:         %5.1f LUFS\n"