Something is wrong with the movie produced by ffmpeg?

When i used the command “ffmpeg -f image2 -r 10 -i /mnt/hgfs/share/Movie/Test%04d.ppm G4Movie.mp4” to produce a vedio file, the size of the pictures is 12.1G, but the vedio file G4Movie.mp4 is only 3.7M, and the G4Movie.mp4 file can not play? how shauld i do?

Assuming the .ppm files have been generated correctly, then this feels more like a question for the ffmpeg community, or its documentation.

@ bmorgan,thanks!