I have a large .avi file from a friend that he wanted lightly edited (changing sound levels basically). I ran it through Handbrake and converted it to MP4 (H.264, 30 frames, AAC codec) then imported it into Pinnacle. I detached the audio from the video then started editing. The first 3 or 4 times through it was synced up perfectly. I had some unrelated and minor inconveniences but I was able to get the work done. I needed to go through it one more time before finalizing it and now when I start the preview the video starts playing but not the sound, and then the sound will start later but delayed. In rough estimations of time based on the timeline it's like this:
start playing - video starts
after ~4 seconds audio starts but delayed
audio plays for ~2 second then stops
after another 4 seconds the audio starts again, delayed
It does this at any point in the timeline, and does it every single time I pause then play, or when I open Pinnacle and load the project and play. I can play the source file in the preview window and it is perfectly fine. I load other projects, even very lengthy ones with many edits, and they play fine.
Attempted troubleshooting:
Restarted Pinnacle several times
Adjusted settings for playback as follows
Quality - Fastest Playback
Playback Optimization - off
and also Playback Optimization - on with most aggressive setting then letting the entire video render
Closed background processes that I could (despite the fact that none of my hardware is even getting close to max, CPU, memory, etc all has plenty left to give)
None of this is working. I'm having no other audio or video issues on other projects or in other applications.