x264: set timebase even if we don't get framerate
x264: set timebase even if we don't get framerate

Pointed by Steinar Gunderson

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc