That's a startup error, it has nothign to be with OSClass but with your PHP installation/configuration.
The php.ini file is trying to load a library (ffmpeg.so) which does not exists (or is not readable).
You could fix it in the following ways :
A.- Modify php.ini to not include that library (if you don't want to/ need it anymore)
or
B.- Make readable/available that library (if you want to have it)
or
C.- modify oc-admin/plugins.php, comment lines 81 and 109, from (line 81)
register_shutdown_function(array($this, 'errorHandler'), $pn, 'install');
to
//register_shutdown_function(array($this, 'errorHandler'), $pn, 'install');
and
from (line 109)
register_shutdown_function(array($this, 'errorHandler'), $pn, 'enable');
to
//register_shutdown_function(array($this, 'errorHandler'), $pn, 'enable');
In tha last case (C), the error will be still there, but you will not see it, so we recommend you to proceed with A or B options, also in C, in the next update of OSClass, you will have to modify again that file (plugins.php)