I used Hamster Video Converter because it's free and I'm cheap. There are plenty of other options that will give you better control, play around and test a few.
You should also take the quality down as low as you dare for streaming online and Hamster doesn't do that very well. This one I dropped the quality to low and dropped the bitrate to 100 and it still came out a bigger file size than the original.

I also prefer to upload the video separately and use a placeholder to point at the file instead of embedding it into Xara. It makes uploading edited content so much quicker and I've convinced myself the page loads faster when it's live (pretty sure I'm delusional on that point though).

Just because files end in mp4 doesn't mean they're all the same, mp4 is just a container, it's what's inside that makes the difference. A few years ago I spent more time asking people with different mobiles to test a video than I did in making the thing, Apple was the pain in the bum then.