[FFmpeg-soc] making moving and zooming effect

[Oleksandr Bondar]

>
> And thinking harder at it, yes it should be possible to implement a
> filter cropping a given (eventually variable) area in the input video
> and scaling it to a fixed output size, for example to implement a Ken
> Burns effect.
>

to get simple version of Ken Burns only overlay effect with dynamic x and y
coordinates is needed.
1. scale video to bigger size then original
2. slowly to move video

Should I take setpts filter as a start point for overlay extending, as it
has N function in parameter?