af_volume: add detach option

Maybe this should be default. On the other hand, this filter does
something even if the volume is neutral: it clips samples against the
allowed range, should the decoder or a previous filter output garbage.

2 files changed, 10 insertions, 0 deletions

diff --git a/DOCS/man/en/af.rst b/DOCS/man/en/af.rst
index 98d33b8f15..81e0d8cfef 100644
--- a/DOCS/man/en/af.rst
+++ b/DOCS/man/en/af.rst
@@ -301,6 +301,12 @@ Available filters are:
     ``s16``
         Force S16 sample format if set. Lower quality, but might be faster
         in some situations.
+    ``detach``
+        Remove the filter if the volume is not changed at audio filter config
+        time. Useful with replaygain: if the current file has no replaygain
+        tags, then the filter will be removed if this option is enabled.
+        (If ``--softvol=yes`` is used and the player volume controls are used
+        during playback, a different volume filter will be inserted.)
 
     .. admonition:: Example
 
diff --git a/audio/filter/af_volume.c b/audio/filter/af_volume.c
index 4abbded822..31f9653e6f 100644
--- a/audio/filter/af_volume.c
+++ b/audio/filter/af_volume.c
@@ -39,6 +39,7 @@ struct priv {
     int rgain_clip;             // Enable/disable clipping prevention
     int soft;                   // Enable/disable soft clipping
     int fast;                   // Use fix-point volume control
+    int detach;                 // Detach if gain volume is neutral
     float cfg_volume;
 };
 
@@ -136,6 +137,8 @@ static int control(struct af_instance *af, int cmd, void *arg)
                     s->rgain = MPMIN(s->rgain, 1.0 / peak);
             }
         }
+        if (s->detach && fabs(s->level + s->rgain - 1.0) < 0.00001)
+            return AF_DETACH;
         return af_test_output(af, in);
     }
     case AF_CONTROL_SET_VOLUME:
@@ -209,6 +212,7 @@ struct af_info af_info_volume = {
         OPT_FLAG("replaygain-clip", rgain_clip, 0),
         OPT_FLAG("softclip", soft, 0),
         OPT_FLAG("s16", fast, 0),
+        OPT_FLAG("detach", detach, 0),
         {0}
     },
 };