The format you need for your dvd player depends entirely on its capabilities. Many dvd players have divx compatibility these days, which means you could use xvid or divx video codecs—usually in an avi container file. Going from H264 to divx or xvid would mean an increase in size of about 40% to maintain maximum quality. You will lose some quality in any conversion however.
A few new players will have support for H264 in mp4 or mkv files. As long as they are not high definition files, these rather rare players could be used. For those, you just burn the mp4 files as data onto a blank dvd.
So, you need to find out exactly what you have in your video files, and you need to learn what types of files your current player can handle. Even minor variations in resolution, frame rate or type of audio can cause problems…so best to know what your player wants and stick to that.
You can examine your current mp4 files with MediaInfo. It is a free program that will tell you exactly what you’ve got in the way of codecs and other specifications. http://mediainfo.sourceforge.net/en
Make certain to opt out of installing Open Candy when you install MediaInfo. I find the Tree view within MediaInfo to be the most informative.
If you need to convert mp4 to xvid avi files, you can do this with lots of different programs. WinFF or AviDemux can do this, for example. Both are free to download and use.