vlc_block: Mention about what discontinuity means
vlc_block: Mention about what discontinuity means

No timeline change, but possible missed blocks.

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