Fix build with mingw-w64

The maximum bitrate of the file is not allowed to become zero. If it
is then playback in WMP12 and Silverlight does not work. The actual
value for maximum bitrate does not really matter in these cases as
long as it is not 0.

Make sure the context callback is registered only after the stream
is created, and unregistered before the stream is destroyed. This
should fix a potential assertion failure when stopping audio.

And convert tabs to 4 spaces according to code guidelines.

This atom can store an optionnal aspect ratio.

It fixes #3531 (DV inside mov)

All of them should be gone, except one.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Signed-off-by: Laurent Aimar <fenrir@videolan.org>