App freeze when output file exists

[lkischler]

When I try to get snapshot and output file just exists conversion will freeze. I expect some exception or break with error.

[tomaszzmuda]

Done.
Now before the FFmpeg process starts, it's validate if output file exists.
If exists return IOException.
Commit link

EDIT
Added "-n" option to Conversion. It's added in every call except when your own params are passed in.
The "-n" flag defines if ffmpeg should immediately stop when destination file exists.