Here, there will be more tips about, especially how to deal with multi compositions.
Here is the work flow:
1-Render out your compositions one by one to Quicktime-> PhotoJPG (.mov file)
(Turn OpenGL on if your graphic card supports- it helps rendering times)
At this step : check your output footage if anything is wrong, correct it.
2-Use MyFFVideoConverter to convert mov (Quicktime : PhotoJPG) to MP4 (MPEG4) files with a high videobitrate (for good quality) (above 20000 is recommended)
*This (MyFFVideoConverter ) Freeware is awesome ! But it doesn't support joining files..Yet! Here is the good news: The author of the software wrote me that in about 2-3 months his new editor software will be ready ! Waiting for it.
3-Use Machete Video Converter (not the Lite one - unfortunetely this software is not free) to join the MP4 files into a single movie file. Machete won't re-encode your MP4 files (which is very good)
p.s. The mp4 joiner softwares that i've tried that has failed working or re-encoded or made a corrupted output are : yamb, mp4joiner, format factory, open video joiner, avidemux, free video joiner, mymp4box gui