[Mp4-tech] Timecode in H.264 ?

[Olivier Amato]

Dear experts,
I wonder if there is a way to handle timecode in H.264 as
it is possible in a MPEG-2 Video elementary stream ( 
group_of_pictures_header() > time_code ) ?
If this is possible, I'm then looking for a tool able to modify timecode 
informations into an existing H.264 bitstream in order to start it at a 
specific timecode.
Thanks in advance.
Olivier