Convert Humax recordings to mp4

I have some recordings on my Humax HDR Fox T2 that i'd like to convert to mp4 video so I can put them on the ipad. For each recording, i have four files, eg:

  13K  Hey Duggee_20160217_0741.hmt
 330K  Hey Duggee_20160217_0741.nts
  43K  Hey Duggee_20160217_0741.thm
 127M  Hey Duggee_20160217_0741.ts

Judging by the file size, it looks like the .ts file is the video data, I don't know what the other files are for. I've tried loading the .ts file into Handbrake and VLC and they don't seem to recognise it. I've also tried converting it with ffmpeg, and get this error message back:

Hey Duggee_20160217_0741.ts: could not find codec parameters

Do I need to read something from the other files? Is there some encryption perhaps? Grateful for any advice. I'm using Linux btw.

Max