Problem with vlc library on QT application

Hi everibody,
I need to stream a video on my Qt application made by several frame (via
udp, http, ecc..). The vlc-library is correttly linked on the application.

When the application run and the stream is started, I've the follow
error message:
"[#########] main decoder error: no suitable decoder module for fourcc `h264'.
VLC probably does not support this sound or video format."
or similar errore message, depending on video's format.
If I run a small application with a singular Qt frame, all it's ok
(same video, same connection). So, small application OK, big application error, same window for the QFrame that receives and play the stream.

Anyone have an idea?
Thanks in advance.