Bitrate is more important than resolution.
Lowered the frame rate and video bit rate as much as possible in the editing software without ruining the quality (software more suited to a still image could do even better). It's a still image so you could have below 1 fps, although Vegas kept crashing during the render if I didn't give it at least 4 fps.
The audio uses a lower sample rate, because it doesn't really affect it that much and you don't need high quality audio to get the joke.>is it due to better video compression?
I could convert to webm and it would probably be better but no this is an mp4 just using a lower bitrate and frame rate. Most frames in typical video codecs are only concerned with the pixels that changed since the previous frame, so on a still image you should be able to get a low bitrate without ruining the quality. IDK how to adjust how often the keyframe is rendered, but you could reduce that as well. I think there are even video codecs that just use a static image instead of rendering it as a video at all.