Video with transparent background file-size issue A client asked me to do an animated product visualization in 3D and then render out the animation in 4K with a transparent background to put on their website. The animation is done but if I want to export it without background I realized that Quicktime is the only option. The 4-sec video then becomes 1,8GB in size! Is there any way around this or do I have to tell them that we can't go with 4K? or can I compress it or use some other format? The animation is also choppy in the video exported without background. When I render out an MP4 with the background it runs smoothly.
Transparent video on the web is possible, but it's going to only work for users with modern browsers.  You'll need to export in two different codecs - one for Chrome users, one for Safari.
From this site:

Safari supports HEVC with alpha, Chrome does not.
Chrome supports VP9 with alpha, Safari does not.

You need to export an HEVC with alpha channel for Safari.
You need a .webm VP9 codec with alpha for Chrome.
The animation codec you've exported at is not designed for web publishing.  It's a lossless very large codec designed for editing or archiving your finished project before you use it to make a smaller lossy version to go on the web.
This is how to make the webm using ffmpeg
ffmpeg -i &quot;movie-prores.mov&quot; -c:v libvpx-vp9 movie-webm.webm

I would recommend also exporting a &quot;fallback version&quot; for browsers that can't cope with transparent video (as a normal h264 mp4 or webm).