I first posted this on the QNAP forum, where several suggestions were to post it also on the Twonky Forum.
As the issue described is not quite the same as the problem here:
I have created a new topic:
In case someone else suffers the same frustration I am posting this info:
Twonkymedia v8.2 causes a problem streaming to a Samsung TV (in my case a UEH6400). The symptom is that files that use to play no longer play and you get a message on the TV "cannot play file type" or similar.
The files involved are all mp4 files encoded with MPEG4 for video and AAC for sound. The crazy thing is that not all files are affected, it seems to be to do with the exact encoder used for the video stream, (e.g Level 1,2 etc.). Files encoded with H.264 are not affected.
As I have hundreds of files in my library, built up over many years, I did not want to recode the files or use transcoding. I use "old fashioned" MPEG4 as it is supported by some of the older devices we have that do not support H.264. The saving in file sizes by using H.264 is marginal.
I discovered the problem (eventually!) by isolating which end the problem was occurring. There had been a firmware update on the Samsung TV and I at first thought that this was the problem. I could still stream everything using Twonkymedia 8.2 on other devices, the problem was solely on the Samsung TV.
I turned on the native DLNA app on the QNAP and told it where to scan the files to build the library. This took forever, but eventually completed. All files then streamed without error on the Samsung TV using the QNAP DLNA server.
I then removed Twonkymedia 8.2 and installed 8.1.1. All files then stream correctly with no errors on the Samsung TV.
The conclusion is that something is broken in Twonkymedia 8.2, but what it is I do not know. I know that Twonky has a history of problems with mp4 files, though I have personally never had a problem in the past.
The result is that if you have a lot of mp4 video files and a Samsung TV, I would recommend sticking with Twonkymedia 8.1.1 and ignoring the update notification message you will continually receive in the App Centre on the QNAP.