How to convert large .mp4 file (~1.5GB) to .gif without my iMac crashing?

As it says in title. I couldn't find a way to convert it with a file conversion system already on my computer using a Google search, and nor could I find any online converters without a size limit. Eventually I did find a website which recommended uploading it to Keynote as a one-slide presentation and saving it as a .gif, but I suppose my computer, as it's quite old, couldn't handle downloading it and crashed. What would be a good way to convert it with minimal stress on my system? Download time isn't a problem as long as it gets done.