mfra atom contains two leaf atoms, 'tfra' and 'mfro'. The first one
provides file offsets of the chunks in a isml file.

mfra atom support will not help Smooth Streaming support in VLC (at
least for the client part), but can be useful for other
purposes, e.g. to enable VLC to play a "raw" isml file.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>