Henrik Gramner authored Oct 22, 2017 and Anton Mitrofanov committed Dec 24, 2017

swscale can read past the end of the input buffer, which may result in
crashes if such a read crosses a page boundary into an invalid page.

Work around this by adding some padding space at the end of the buffer when
using memory-mapped input frames. This may sometimes require copying the
last frame into a new buffer on Windows since the Microsoft memory-mapping
implementation has very limited capabilities compared to POSIX systems.