changes:
New optimizations have been provided for SSE2 and ARM instruction sets,
while a lot of warnings triggered by recent compiler changes have been
fixed.
A new function has been added to guess the aspect ratio of streams where
it is not properly coded. Also it is now possible to retrieve the value
of the MPEG-2 repeat_first_field flag, and to be notified when the
sequence header of a stream changes (eg. aspect ratio on-the-fly changes).
