[FFmpeg-user] How to slow down video playback?

[Virgil Stokes]

I have used FFmpeg to extract PNG images for each frame of some short AVI files. 
These AVIs were created for a research project in which a person's movements 
were recorded over about 2 seconds at 25 fps.  These extracted images are then 
processed and graphical objects are often superimposed on them; but, the PNG 
images are always kept at the same size (720 x 576 Px).

I use FFmpeg to merge these new PNG images back into an AVI file; then use Miro 
to convert the AVI to an MP4.The problem that I have been unable to solve is 
that when I playback this MP4 file in an HTML5 video player with FireFox (or 
Chrome or IE) they are so short that the viewer has little chance to examine 
them.  I would like to be able to show them frame-by-frame; but, this apparently 
is a rather difficult problem for the HTML5 video player.

Is it possible to use FFmpeg to create a very slow AVI (e.g. 1 frame per second) 
or an MP4 file directly, that would allow the user to study the individual 
images? I would be glad to provide one of these short AVIs for testing purposes 
if needed.

--V