When putting a MP4 movie onto a USB, is it possible to have soft titles? (on/off)
Should be able to add .srt subtitles to an mp4. See DrageMester's reply in the VidCoder thread: http://club.myce.com/f3/vidcoder-updates-337636/index2.html#post2742787
Playback depends on the capability of your player I would think.
Indeed it does. Many players (e.g. Sony televisions) only support external SRT subtitle files for MP4, not internal (embedded) subtitles.
That's called subtitles not "soft titles".