Proper error messages for Audio2MIDI script

diff --git a/scripts/vamp_audio_to_midi.lua b/scripts/vamp_audio_to_midi.lua
index b7db5d6dcec147a7598c5fe8ef2f8910504daa87..2f9101196c20cfa1bdb7bd6d8c00679f4ffd599b 100644 (file)
--- a/scripts/vamp_audio_to_midi.lua
+++ b/scripts/vamp_audio_to_midi.lua
@@ -18,7 +18,7 @@ function factory () return function ()
        local sr = Session:nominal_sample_rate ()
        local tm = Session:tempo_map ()
        local vamp = ARDOUR.LuaAPI.Vamp ("libardourvampplugins:qm-transcription", sr)
-       local midi_region
+       local midi_region = nil
        local audio_regions = {}
        local start_time = Session:current_end_sample ()
        local end_time = Session:current_start_sample ()
@@ -41,7 +41,16 @@ function factory () return function ()
                        midi_region = r:to_midiregion()
                end
        end
-       assert (audio_regions and midi_region)
+
+       if #audio_regions == 0 then
+               LuaDialog.Message ("Polyphonic Audio to MIDI", "No source audio region(s) selected.\nAt least one audio-region to be analyzed need to be selected.", LuaDialog.MessageType.Error, LuaDialog.ButtonType.Close):run ()
+               return
+       end
+       if not midi_region then
+               LuaDialog.Message ("Polyphonic Audio to MIDI", "No target MIDI region selected.\nA MIDI region, ideally empty, and extending beyond the selected audio-region(s) needs to be selected.", LuaDialog.MessageType.Error, LuaDialog.ButtonType.Close):run ()
+               return
+       end
+
        midi_region:set_initial_position(start_time)
        midi_region:set_length(end_time - start_time, 0)