FFMPEG and Python

I have written a Python script that, at one point, needs to convert an avi file into an mp4 file. I have been using an ffmpg call outside of Home Assistant in the following format:

subprocess.call([‘ffmpeg’, ‘-y’, ‘-i’, avifile, outputfile])

I am now integrating this into home assistant. It appears that “import FFMPEG” does integrate some form of the HA FFMPEG integration. However, I am not sure that this supports the conversion functionality and, if it does, I cannot find the correct format of such a python command. Any ideas?