Of course make sure Samsung TV (B-series) is showing as selected for this device in Serviio Console.
It will help if you post a debug log ...or at least the output of "%ProgramFiles%\Serviio\lib\ffmpeg.exe" -i "\path\to\the\unplayable\file.mp4" with the unplayable file path replaced as appropriate.
or use mediainfo on one on the mp4's and copy the text into a [code ] bracket without the spaces [/code ] and post it. Not all mp4 are the same, not all audio is the same. Hopefully it's easily solved by someone here. I don't have that tv so don't know.
Yes, need the media info so we can determine what video and audio codecs are in the MP4 container.
Dan
Panasonic ST30 Plasma, Samsung JU7100 4K TV, Sony BDP-S3500, Sharp 4K Roku TV, Insignia Roku TV, Roku 4, Ultra and Stick, Yamaha RX-V583 AVR. Primary server: Intel i5-6400, 8 gig ram, Windows 10 Pro, 18 TB hard drive space | Test server Windows 7 Home Premium, AMD Phenom II X4 965, 8 gig ram