Fix for ffmpeg return code false positive errors

[raivisdejus]

This is a fix for ffmpeg return code errors that tend to happen only on windows when some of the binary output from the ffmpeg call spills over in the terminal and is interpreted as non-zero return code from the process.

Below is an example of a ffmpeg call on a system that exhibits this problem.

Binary data has corrupted the terminal formatting and part of it sits as input.