Reset last metadata on new track by default. Add a source method to

change the default.

src/core/lang_source.ml

@@ -156,7 +156,16 @@ let source_methods =
       "Indicate if a source is ready to stream. This does not mean that the \
        source is currently streaming, just that its resources are all properly \
        initialized.",
-      fun (s : Source.source) -> val_fun [] (fun _ -> bool s#is_ready) );
+      fun s -> val_fun [] (fun _ -> bool s#is_ready) );
+    ( "reset_last_metadata_on_track",
+      ([], ref_t bool_t),
+      "If `true`, the source's `last_metadata` is reset on each new track. If \
+       a metadata is present along with the track mark, then it becomes the \
+       new `last_metadata`, otherwise, `last_metadata becomes `null`.",
+      fun s ->
+        reference
+          (fun () -> bool s#reset_last_metadata_on_track)
+          (fun b -> s#set_reset_last_metadata_on_track (to_bool b)) );
     ( "buffered",
       ([], fun_t [] (list_t (product_t string_t float_t))),
       "Length of buffered data.",

src/core/source.ml

@@ -425,6 +425,14 @@ class virtual operator ?(stack = []) ?clock ?(name = "src") sources =
     initializer
       self#on_before_streaming_cycle (fun () -> on_track_called <- false)
 
+    val mutable reset_last_metadata_on_track = Atomic.make true
+
+    method reset_last_metadata_on_track =
+      Atomic.get reset_last_metadata_on_track
+
+    method set_reset_last_metadata_on_track =
+      Atomic.set reset_last_metadata_on_track
+
     val mutable on_track : (Frame.metadata -> unit) List.t = []
     method on_track fn = on_track <- fn :: on_track
 
@@ -436,6 +444,7 @@ class virtual operator ?(stack = []) ?clock ?(name = "src") sources =
     method private execute_on_track buf =
       if not on_track_called then (
         on_track_called <- true;
+        if self#reset_last_metadata_on_track then last_metadata <- None;
         self#set_last_metadata buf;
         let m = Option.value ~default:Frame.Metadata.empty last_metadata in
         self#log#debug "calling on_track handlers..";

src/core/source.mli

@@ -216,6 +216,9 @@ class virtual source :
        (** The source's last metadata. *)
        method last_metadata : Frame.metadata option
 
+       method reset_last_metadata_on_track : bool
+       method set_reset_last_metadata_on_track : bool -> unit
+
        (** Register a callback to be called on new metadata *)
        method on_metadata : (Frame.metadata -> unit) -> unit
 

tests/regression/append.liq

@@ -1,26 +1,29 @@
 music = chop(every=1., metadata=[("source", "s1")], sine(amplitude=0.1, 440.))
 
 def next(_) =
-  s = sine(amplitude=0.1, duration=.5, 880.)
-  metadata.map(insert_missing=true, fun (_) -> [("source", "s2")], s)
+  sine(amplitude=0.1, duration=.5, 880.)
 end
 
 s = append(music, next)
 
 count_s1 = ref(0)
 count_s2 = ref(0)
 
-s.on_metadata(fun (m) -> begin
-  s = m["source"]
-  if s == "s1" then
-    ref.incr(count_s1)
-  elsif s == "s2" then
-    ref.incr(count_s2)
-  end
+s.on_track(
+  fun (m) ->
+    begin
+      s = m["source"]
+      if
+        s == "s1"
+      then
+        ref.incr(count_s1)
+      else
+        test.equal(m["source"], "")
+        ref.incr(count_s2)
+      end
 
-  if count_s1() > 2 and count_s2() > 2 then
-    test.pass()
-  end
-end)
+      if count_s1() > 2 and count_s2() > 2 then test.pass() end
+    end
+)
 
 output.dummy(s)