Loop playback and host synchronization

[satoshi-szk]

Thank you for releasing such a wonderful library. I am making good use of it.

I am trying to create a sequencer plugin, but I am encountering some issues. I'm not sure if it's a bug or an intentional design, so I decided to post here in the discussion first.

Plugin I want to create

I want to make the functionality of the StepSequencerDemo available as a DAW plugin. In other words, I want to loop-play the Edit while synchronizing with the host's playback position.

What I tried

I set it up to synchronize with the host using ExternalPlayheadSynchroniser, similar to EngineInPluginDemo.h. At the same time, I set up the loop as follows:

te::BeatRange loopBeatRange {{}, te::BeatDuration::fromBeats(4)};
te::TimeRange loopTimeRange = edit->tempoSequence.toTime(loopBeatRange);
edit->getTransport().setLoopRange(loopTimeRange);
edit->getTransport().looping = true;

The behavior I expect is that, regardless of the host's playback position, the first measure (4 beats) of the Edit will loop-play. However, when I tested it with Ableton Live and Reaper, only the first 4 beats of the Edit played, and then noise occurred.

Questions

• Is this behavior an intentional design or a bug?
• To achieve the behavior I desire, it seems like I should define a class similar to ExternalPlayheadSynchroniser myself. Is this the right direction, or is there an existing class that I might have overlooked that can achieve this?

[satoshi-szk]

To be clear, I want to achieve the following synchronization.

Host Playhead	Edit Playhead
0	0
1	1
2	2
3	3
4	0
5	1
6	2
7	3
8	0

And looping around a single clip is not what I'm seeking for. My plugin plays a pattern which contains multiple audio clips.

[satoshi-szk]

Hi everyone,

I was wondering if anyone had a chance to look at this discussion? I'm still looking for some input on this matter and would greatly appreciate any thoughts or suggestions.

Thank you in advance!

[drowaudio]

Have you tried the EngineInPlugin demo directly to see if it has the behaviour you require?
I think that should loop as you’re describing?

If there are some minimal changes that can be made to that example that exhibit the problem that’s probably the best place for us to start. Thanks.

[satoshi-szk]

Thank you for taking the time to address my question.

I modified EngineInPluginDemo.h as shown below, but I was unable to get it to loop.

diff --git a/examples/EngineInPluginDemo/EngineInPluginDemo.h b/examples/EngineInPluginDemo/EngineInPluginDemo.h
index 9c1f130ee39..91e78d104c6 100644
--- a/examples/EngineInPluginDemo/EngineInPluginDemo.h
+++ b/examples/EngineInPluginDemo/EngineInPluginDemo.h
@@ -199,7 +199,10 @@ private:
 
             setupInputs (*edit);
             setupOutputs (*edit);
-            create4OSCPlugin (*edit);
+            EngineHelpers::loadAudioFileAsClip(*edit, {"/Users/YourName/Develop/JUCE/examples/Assets/cello.wav"});
         }
 
         te::Engine engine { ProjectInfo::projectName, nullptr, std::make_unique<PluginEngineBehaviour>() };

The actual behavior:

• The cello sound plays only once at bar 1, but does not play at bar 5, 9, 13, etc.
• The timecode display loops (1, 2, 3, 4, 1, 2, 3, 4...).

The test environment:

• Tracktion Engine v3.1.0
• macOS Sonoma 14.4.1
• arm64
• Ableton Live 12 Standard & Reaper v7.15
• I built and tested the EnginePluginDemo_VST3 target.

Questions:

• In EngineInPluginDemo.h, I did not find any code related to loop settings. Is the loop state (enabled/disabled) and the loop range configured implicitly somewhere?
• Why does the timecode display loop, while the sound does not? Which one is the expected behavior?

[satoshi-szk]

Hi @drowaudio !

Just a friendly ping about my question on the EngineInPluginDemo looping behavior. Wondering if you had any insights on why the timecode loops but the audio doesn't?

Thanks for your time!

[julianstorer]

If you look at what ExternalPlayheadSynchroniser does, it just makes the tracktion engine time match that of the host DAW.
What you're asking for is to map the incoming time to a looped position, so you'd need to write your own custom version of ExternalPlayheadSynchroniser that does the mapping you need.

[satoshi-szk]

Thank you for the explanation, @julianstorer. I’ll implement a custom synchroniser mapping the host’s time to a looped position as suggested.
I truly appreciate the effort behind this amazing library. Thanks.