Playing event not in sync when recording to mp4 h264

[Maloupi]

Hi !

I'm transcoding a stream to a file with libvlc.
I'm monitoring the playing event to know when the file start to really recording the stream.
When i'm transcoding to h264 (h264/mp4a/mp4), there is a variable delay between the event fire and the real recording of the file. It may be up to 20-30 sec delay.
If i'm transcoding to div3 (div3/mp3/asf), there is no problem.

Is it normal and due to mp4
or is it a bug
or is there another way to know when the file is really recording ?