These are all needed to use FFmpeg on the worker to render a video from rendered image sequences. - fps: float, the scene FPS - images_or_video: either 'images' or 'video', depending on what's being output by Blender. We don't support using FFmpeg to join chunked videos yet. - output_file_extension: string like '.png' or '.exr', only set when outputting images (since doing this for video requires a lookup table and isn't even being used at the moment).