Fix blank.strip

src/core/operators/noblank.ml

@@ -122,22 +122,24 @@ class strip ~start_blank ~max_blank ~min_noise ~threshold ~track_sensitive
     inherit active_operator ~name:"blank.strip" [source]
     inherit base ~track_sensitive ~start_blank ~max_blank ~min_noise ~threshold
     method fallible = true
-    method private can_generate_frame = (not self#is_blank) && source#is_ready
+
+    method private can_generate_frame =
+      (* This needs to be computed at all times as it makes sure that the
+         source is ready to be ready from in [#output]. *)
+      let is_source_ready = source#is_ready in
+      (not self#is_blank) && is_source_ready
+
     method remaining = if self#is_blank then 0 else source#remaining
 
     method seek_source =
       if self#is_blank then (self :> Source.source) else source#seek_source
 
     method abort_track = source#abort_track
     method self_sync = source#self_sync
-
-    method private generate_frame =
-      let buf = source#get_frame in
-      self#check_blank buf;
-      buf
+    method private generate_frame = source#get_frame
 
     method private output =
-      if source#is_ready && self#is_blank then ignore self#get_frame
+      if source#is_ready then self#check_blank source#get_frame
 
     method reset = ()
   end
@@ -294,7 +296,10 @@ let _ =
   in
   Lang.add_operator ~base:Blank.blank "strip" ~return_t:frame_t ~meth:(meth ())
     ~category:`Track
-    ~descr:"Make the source unavailable when it is streaming blank."
+    ~descr:
+      "Make the source unavailable when it is streaming blank. This is an \
+       active operator, meaning that the source used in this operator will be \
+       consumed continuously, even when it is not actively used."
     (proto frame_t) (fun p ->
       let start_blank, max_blank, min_noise, threshold, track_sensitive, s =
         extract p

tests/regression/GH4163.liq

@@ -0,0 +1,42 @@
+first_blank =
+  metadata.map(
+    id="first_blank", fun (_) -> [("title", "first_blank")], blank(duration=3.)
+  )
+
+after_blank =
+  metadata.map(
+    id="after_blank", fun (_) -> [("title", "after_blank")], sine(duration=10.)
+  )
+
+blank_sequence = sequence(id="blank_sequence", [first_blank, after_blank])
+
+blank_strip =
+  blank.strip(id="blank_strip", max_blank=5., start_blank=true, blank_sequence)
+
+fallback_sine =
+  metadata.map(id="fallback_sine", fun (_) -> [("title", "fallback")], sine())
+
+s =
+  fallback(
+    id="main_source", track_sensitive=false, [blank_strip, fallback_sine]
+  )
+
+# We want to make sure that blank.strip keeps eating the blank source before switching back:
+expected_titles = ["fallback", "after_blank"]
+seen_titles = ref([])
+
+def on_metadata(m) =
+  seen_titles := [...seen_titles(), m["title"]]
+  if
+    seen_titles() == expected_titles
+  then
+    test.pass()
+  elsif list.length(seen_titles()) == 2 then test.fail()
+  end
+end
+
+s = source.on_metadata(id="on_meta", s, on_metadata)
+
+clock.assign_new(sync='none', [s])
+
+output.dummy(s)

tests/regression/dune.inc

@@ -735,6 +735,22 @@
   (:run_test ../run_test.exe))
  (action (run %{run_test} GH4144.liq liquidsoap %{test_liq} GH4144.liq)))
 
+(rule
+ (alias citest)
+ (package liquidsoap)
+ (deps
+  GH4163.liq
+  ../media/all_media_files
+  ../../src/bin/liquidsoap.exe
+  ../streams/file1.png
+  ../streams/file1.mp3
+  ./theora-test.mp4
+  (package liquidsoap)
+  (source_tree ../../src/libs)
+  (:test_liq ../test.liq)
+  (:run_test ../run_test.exe))
+ (action (run %{run_test} GH4163.liq liquidsoap %{test_liq} GH4163.liq)))
+
 (rule
  (alias citest)
  (package liquidsoap)