It appears that with the QTS v4.5.1 upgrade, QNAP have disabled a large majority of the video decoders in the default /usr/bin/ffmpeg which is used by Twonky for generating thumbnails.
I have managed to workaround the issue by performing the following actions:
NOTE: this is only applicable to the manually installed Twonky v8.5.1 and not the QNAP provided version in AppCenter. These are the steps I followed, if you choose to do so yourself then it is at your own risk.
- Open Multimedia Console and enable Multimedia Services if not already enabled
- Install CAYIN MediaSign Player (no need to activate this with a licence)
- Once installation is complete, return to Multimedia Console and disable Multimedia Services if this was your previous state, otherwise leave running. (a notification will advise that CAYIN MediaSign Player has been stopped)
- Get the appdata location for your Twonky installation by entering the following in a browser https://yourTwonkyIPaddress:9000/rpc/get_option?appdata
- Inside AppCenter, stop Twonky Server EU 8.5.1
- Login to an SSH console as admin and change to the appdata directory discovered above, then go up one directory and into a directory called cgi-bin (in my example this folder is '/share/CE_CACHEDEV1_DATA/.qpkg/TwonkyServerEU/cgi-bin')
- Edit the file ffmpeg.location using your preferred editor (in my case vi) and change '/usr/bin' to read '/usr/local/cayin/bin'
- Return to AppCenter and start Twonky Server EU 8.5.1
NOTE: I determined the location of the CAYIN replacement ffmpeg by running 'find / -name "ffmpeg"' from the SSH console. This might be useful if it is installed in a different location on your machine.