When OT was first released, there were actually no working video formats on the macOS release. Not even the mov option, which I found crazy since it's a native mac format. Fortunately that has changed. Unfortunately, AVI is just available on Windows. On macOS, for video, we can render to mov or mp4 or webm formats. From there, you can always load your render into another software to convert it to avi, if avi is really needed.