[Ffmpeg-devel] warning: first frame is no keyframe

[Mat]

Hi all.
I'm using libavformat in 2 applications, video encoding in MP4 [MOV] and 
video decoding in SDL (like ffplay)
When I create a video (I used output_example.c as reference) and I play 
it in ffplay all is ok.
When I play the video with my application I get the warning message:
    warning: first frame is no keyframe
and the first frames are wrong.
I used the example from a link in the FFMpeg site as reference:
    http://www.inb.uni-luebeck.de/~boehme/using_libavcodec.html
because ffplay is not very easy to follow :)
So... is there a way to force the writing of a keyframe on the first frame?
How does ffplay show the first frames if there isn't a starting keyframe?!
Thanks in advance.
-Mat-