Just remembered something,just because a TV is 4k doesn't necessarily mean that it can play 4k files via usb.Every TV has different limits regarding USB playback.I found these manuals for 2 different panasonic professional led tv(one is UHD) & neither of them supports 4k video playback over usb.
*panasonic.net/cns/prodisplays/download/pdf/instructions/TH-55_49_42AF1U_W_Eng.pdf
*panasonic.net/cns/prodisplays/download/pdf/instructions/TH-LFE8U_E_manual_en.pdf
Also as per product page TH-49CX400DX LED LCD TV - Panasonic India it says 4k only supported through hdmi.
View attachment 16918
So my conclusion is that this model does not support 4k playback over usb.