Trouble to get ffmpeg encoding up and running - stops at 95%

Hey, I have recently updated to 1.4 and have now trouble to get the video encoding feature up and running.

I run my site on a Synology Diskstation and use the preinstalled ffmpeg version 2.0.2.

first I had trouble with the scaling factor of -2 which does not seem to be supported by this version and have changed /joomla/administrator/components/com_easysocial/includes/ffmpeg/adapter.php [line: 581] to

        $command .= '-vf "scale=-1:\'min(ih,' . $size . ')\'" ';

but now the encoding starts but stays at 95 % forever.

Sadly I havent found any documentation regarding what ffmpeg version is needed or how to trouble shoot this. I hope you can help.

Attached you will find the logfile