[Guest]

Performing irregular decimation is the cause of your desync. To explain I first describe a simple but extreme case.

Consider a clip with 300 frames played at 30fps. If you decimate every 5th frame (i.e., 60 frames) and play it at 24fps, it will remain in perfect sync. Now consider decimating the first 60 frames and leaving the rest and playing at 24fps. It will start 2 seconds out of sync and gradually regain sync as the movie plays and reach correct sync only at the end.

Yes, it's an extreme example, but it illustrates how irregular decimation can cause desync. If you set a large cycle and then decimate irregularly in the cycle, you will get desync.

Every time you decimate a frame before one is due for decimation according to the regular cycle, you create ~33ms desync. Every time you neglect to decimate one you create ~33ms desync the other way. You will have a random walk of total desync and the longer the cycle the bigger the desync can become.

The problem is that the audio was synced to this clip with irregular duplicates. You understandably want to get rid of all the duplicates. But you can't, because you cannot avoid the resulting desync.

Also, you will get an oddball framerate by decimating like that.

I recommend choosing some reasonable cycle size so that the desync cannot accumulate too much and then just accept some remaining dups. You cannot get a perfect result.

Finally, you don't need two field matchers.