How to best convert Flash compatible mp4 files with FFMPEG?

Question

I am trying to convert different files to a flash compatible .mp4 file with ffmpeg, but I can't seem to get it to work. Of course the objective is to get the greatest quality with the smallest file size.

So far I have this, which works, but it doesn't play in a flash player for some reason. The result isn't that great, how can I improve this conversion?

This is the command I'm using:

ffmpeg -i input.file -f mp4 -vcodec mpeg4 -r 25 -b 560000 -s 610x340 -acodec aac -ac 2 -ab 64 -ar 44100 output.file