VST Effect buffer not being flushed

Operating System Info

macOS 13

Other OS

No response

OBS Studio Version

29.1.3

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/1oaVkKE2QUyRViLI

OBS Studio Crash Log URL

No response

Expected Behavior

I added a VST plugin filter to a media source in a scene in order to introduce an audio delay (https://www.voxengo.com/product/sounddelay/). This performs as expected, but once you have already played that media to some point, subsequent plays by stopping and restarting, moving the position on the media controls, or by changing scene from another back to this scene will start the audio playback from where it was in the prior playback. I believe this is coming from the effect buffer and the effect is resuming with the previous buffer contents - in the case of a delay then previous audio from the length of the set delay will precede the current playback.

In order to produce a 'clean' playback then the VST buffer needs to be flushed on scene change, restart playback etc.

Current Behavior

Once you have already played that media to some point, subsequent plays by stopping and restarting, moving the position on the media controls, or by changing scene from another back to this scene will start the audio playback from where it was in the prior playback. I believe this is coming from the effect buffer and the effect is resuming with the previous buffer contents - in the case of a delay then previous audio from the length of the set delay will precede the current playback.

Steps to Reproduce

1. Create a scene with a video clip media source
2. Add VST effect filter such as https://www.voxengo.com/product/sounddelay/
3. Set up a delay and play the media source
4. Stop and restart the media source at a point where there is some audio playing
5. When the media restarts from the beginning then it will start by playing existing audio from the VST buffer (ie. audio from later in the clip) until the buffer fills from the fresh playback.
   ...

Anything else we should know?

No response

Reproduce the issue using the listed macOS setup, media source, and VST delay plugin, then inspect the linked OBS log. Trace the VST effect lifecycle when playback stops, restarts, seeks, or the scene changes. Done means restarting playback or returning to the scene produces no audio left in the previous effect buffer.