Cannot run program "ffmpeg": error

Fresh installation ver.1.6.0 on Raspberry Pi Linux. Installation had been done following instruction on serviio.org.
Library update stopped after ~162000 entries, but definitely some tens of thousand are still missing.
Restarting serviio.sh doesn't restart library update, even the "Force update" button in the console doesn't show any reaction.
Log file frequently says

2016-04-05 22:31:19,222 ERROR [ProcessExecutor] Fatal error in process starting: Cannot run program "ffmpeg": error=2, File or Directory not found
java.io.IOException: Cannot run program "ffmpeg": error=2, File or Directory not found
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
at org.serviio.external.ProcessExecutor.run(ProcessExecutor.java:136)
Caused by: java.io.IOException: error=2, File or Directory not found
at java.lang.UNIXProcess.forkAndExec(Native Method)
at java.lang.UNIXProcess.<init>(UNIXProcess.java:248)
at java.lang.ProcessImpl.start(ProcessImpl.java:134)
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)

Went anything wrong during installation? How should I proceed?

Thanks for support.
Willy from Germany