No subtitles in MP4 files

Hey guys.
I'm a newbie in all this, and after having used Twonky I decided to give Serviio a try. But I realized they both have the same issue (which by now I'm starting to think it's TV related.. )
I have some video files in . MP4 and other in XVid (.avi). For the .avi files, the TV allows me to see the subtitles (via "Option" button on the remote), but not for the MP4 files.
Is there something I can do? Maybe changing the profile on Serviio, or something?
My TV is a Panasonic Viera TC-L42ET5B. I'm running Sertviio 1.2.1.

Thanks,
Tiago

[zip]

AFAIK the Viera doesn't support external subtitles for mp4's. So you can use the burned-in subtitles option with the option of Only when required (it will not transcode your avi files, but will mp4 files, when there are subtitles available)