Bug 510047

Summary: Wrong LADSPA control indexes when plugin exposes audio ports before control ports
Product: [Applications] kdenlive Reporter: sachzwang.kdebugs
Component: Audio Effects & TransitionsAssignee: Jean-Baptiste Mardelle <jb>
Status: REPORTED ---    
Severity: normal    
Priority: NOR    
Version First Reported In: 25.08.1   
Target Milestone: ---   
Platform: Debian stable   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description sachzwang.kdebugs 2025-09-29 12:30:50 UTC 
I had problems with several LADSPA plugins. Some seem to work, some don't. I dug a little deeper with the DeepFilterNet plugin: https://github.com/jacksongoode/DeepFilterNet

When changing control values in the Kdenlive UI, the DeepFilterNet plugin gets sent the wrong control indexes. The index is always off by 4, which I verified with a log statement in the plugin code. The DeepFilterNet plugin exposes 4 audio ports (stereo in, stereo out; index 0 to 3) and several control ports. The DeepFilterNet plugin works in Audacity. Other plugins, such als Rubber Band Stereo Pitch Shifter, work also in Kdenlive.

Rubber Band Stereo Pitch Shifter and other LADSPA plugins export control ports first, then audio ports.

Kdenlive seems to confuse the port indexes when plugins expose audio ports before control ports.


SOFTWARE/OS VERSIONS
Operating System: Debian GNU/Linux 12
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Kernel Version: 6.1.0-39-amd64 (64-bit)
Graphics Platform: offscreen
Processors: 16 × AMD Ryzen 7 3700X 8-Core Processor
Memory: 47.0 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3060/PCIe/SSE2
Comment 1 sachzwang.kdebugs 2025-09-29 12:32:35 UTC 
https://bugs.kde.org/show_bug.cgi?id=442197 seems related. "listplugins" and "analyseplugin" can be used to check the ordering of audio/control ports.
Comment 2 sachzwang.kdebugs 2025-09-29 13:03:19 UTC 
I reordered the ports in the plugin to expose the control ports first, and the problem is gone. So I'm pretty sure the issue lies there. I don't know enough about Kdenlive internals to create a patch.