Nice! I think you can approximate timing somewhat, by making your web server create the "jpeg" on the fly and send it to the client in timed chunks. The source could even be a webcam, so the "jpeg" would go on forever.
A lot of IP cameras already do this via https://en.wikipedia.org/wiki/Motion_JPEG
You can do this with the gif too, I have once created a toy cgi that combined a gif sending one frame at a time with an image map allowing you to Remote Desktop with no JavaScript and click around. JPEG may have been a better choice, maybe I’ll revisit this.
There are already webcams which do this- but they use a mime trick for 'multipart/x-mixed-replace'.
That's basically the server telling the client 'That data I just sent you, well now replace it with this new thing'.
No JavaScript needed, and can work with plain http and jpeg