It's hard to tell what you are trying to do, chances are that you haven't the slightest idea either, but I'm going to take a shot in the dark:

is the problem that you cannot reliably tell when has Asterisk finished with the recording?

In that case I'd recommend moving any kind of postprocessing out of the dialplan, AGI handlers etc. Instead, do it in a completely separate process, and use inotify with a IN_CLOSE_WRITE event mask to to monitor for files. In my experience once Asterisk closes a recording it doesn't reopen it, so it's safe to do any postprocessing steps (transcoding, speech-to-text, uploading etc.) on it.