ffmpeg problem with jDownloader

hi Guys

have trisquel 8.0 / mate + jdownloader installed.

Unfortunately, the jD Download Manager blocks if I have one
Load music file - "ffmpeg" will be installed ..
but can not be used.
The download is blocked

ffmpeg was also installed manually via terminal -
the charging function is still blocked

how or where can I find a shot, or
which tool to install

thank you, best regards