Indeed. ffmpegX looks like the way to go.
Here are some pointers to get you started:
1.) Download and install FFmpegX
. Make sure you read all the information at versiontracker, you have to install other components too in order for ffmpegX to work.
2.) Launch ffmpegX, click "open...", and choose your .mp4 file.
3.) In the "to" box under "target format" on the right, choose "DVD mpeg2enc"
4.) Click on the "video" tab, choose "1" CD of "DVD 4GB" in the drop-down menus on the left, and click the "rate" button. This will automatically choose an appropriate bit-rate. Make sure the dimensions and frame rate on the right are correct.
5.) Click audio and choose .ac3 from the drop-down. Select the bitrate etc. that you want.
6.) Click on "options" tab, and on the right, choose profile as "DVD" and click the "author as" tick box (at the bottom) and choose "DVD (VIDEO_TS)"
7.) Click back to summary, press "save as..." and choose a destination location and file name.
8.) Press encode. When it is done, you should find a new folder, whose name ends .DVD, in the destination that you chose. That folder should contain an "AUDIO_TS" folder and a "VIDEO_TS" folder.
9.) Launch Toast.
10.) Select the Video tab, and in the drawer on the left, choose "DVD-video from VIDEO_TS", then drag and drop the VIDEO_TS folder created in step 8.) above to the main window.
11.) Burn disc.
This may require some experimentation on your part to get just right. Good luck.