add clip path to video filter
Merge branch 'text' into filter
add filter manager
check whether filter is released
filter.installTo implemention
(un)install filters and tasks in AVThread for internal use

FIXME:
for the case pause next frame, if next frame is called after timeout and
before tryPause, then current frame will still displayed and not the
next frame. which is wrong
uninstallFilter and task implementions
workaround for better default filter drawing position

TODO:
why (0, 0) will not be visible
access context of filter. share common context data
avoid calling QPainter::end() and delete painter multiple times

the whole context is shared before. now only some common data shared,
e.g. painter. we can delete them in each context
TODO: use shared ptr for those common ptr
filter delayed install until AVThread is ready
filter mgr: can not return ref to temp var
default Filter ctor
filter context draw at null rect's position
add a filter example
Merge branch 'filter'
initialize statistics if a output is added. otherwise filter will not
process
qml: fillMode support
filter example: fix wrong position and compile error
restore qpainter state missing