ffmpeg is usually best for those tasks (Spine uses fmmpeg under the covers for some exports). Ask ChatGPT how to do what you need so you don't have to figure out archaic ffmpeg CLI parameters.
I recently needed to export a GIF from Spine, but it was 40MB. After scaling it down and wrecking the colors/etc it was 14MB. I exported with WEBM (at the full size and colors) and it was 600KB! 40MB -> 600KB made me a believer.
