Add global meta setting to amplify. (#4213)

src/core/operators/amplify.ml

@@ -26,7 +26,7 @@ open Source
 let parse_db s =
   try Scanf.sscanf s " %f dB" Audio.lin_of_dB with _ -> float_of_string s
 
-class amplify ~field (source : source) override_field coeff =
+class amplify ~field ~override_field (source : source) coeff =
   object (self)
     inherit operator ~name:"track.audio.amplify" [source]
     val mutable override = None
@@ -63,7 +63,7 @@ class amplify ~field (source : source) override_field coeff =
       else buf
 
     method private set_override buf =
-      match override_field with
+      match Option.map (fun f -> f ()) override_field with
         | Some f ->
             if override <> None then
               self#log#info "End of the current overriding.";
@@ -92,24 +92,26 @@ let _ =
   let frame_t = Lang.pcm_audio_t () in
   Lang.add_track_operator ~base:Modules.track_audio "amplify"
     [
-      ("", Lang.getter_t Lang.float_t, None, Some "Multiplicative factor.");
       ( "override",
-        Lang.nullable_t Lang.string_t,
+        Lang.getter_t (Lang.nullable_t Lang.string_t),
         Some (Lang.string "liq_amplify"),
         Some
           "Specify the name of a metadata field that, when present and \
            well-formed, overrides the amplification factor for the current \
            track. Well-formed values are floats in decimal notation (e.g. \
            `0.7`) which are taken as normal/linear multiplicative factors; \
            values can be passed in decibels with the suffix `dB` (e.g. `-8.2 \
-           dB`, but the spaces do not matter)." );
+           dB`, but the spaces do not matter). Defaults to \
+           `settings.amplify.metadata`. Set to `null` to disable." );
+      ("", Lang.getter_t Lang.float_t, None, Some "Multiplicative factor.");
       ("", frame_t, None, None);
     ]
     ~return_t:frame_t ~category:`Audio
     ~descr:"Multiply the amplitude of the signal."
     (fun p ->
       let c = Lang.to_float_getter (Lang.assoc "" 1 p) in
       let field, s = Lang.to_track (Lang.assoc "" 2 p) in
-      let o = Lang.to_option (Lang.assoc "override" 1 p) in
-      let o = Option.map Lang.to_string o in
-      (field, new amplify ~field s o c))
+      let override_field =
+        Lang.to_valued_option Lang.to_string_getter (Lang.assoc "override" 1 p)
+      in
+      (field, new amplify ~field ~override_field s c))

src/libs/tracks.liq

@@ -61,3 +61,25 @@ def source.drop.metadata(~id=null(), s) =
   let {metadata = _, ...tracks} = source.tracks(s)
   source(id=id, tracks)
 end
+
+let settings.amplify =
+  settings.make.void(
+    "Settings for the amplify operator"
+  )
+
+let settings.amplify.override =
+  settings.make(
+    description=
+      "Default metadata used to override amplification.",
+    "liq_amplify"
+  )
+
+# @docof track.audio.amplify
+def track.audio.amplify(
+  %argsof(track.audio.amplify[!override]),
+  ~override=getter({(settings.amplify.override() : string?)}),
+  v,
+  t
+) =
+  track.audio.amplify(%argsof(track.audio.amplify), v, t)
+end