I'm using an Apple TV for a while now and I never had this problem before. I stream mp4 files to my Apple TV 3 from my Synology NAS using DS video station. I mux in the subtitles myself using programs like Subler and MP4Tools from SRT to Tx3g. But when I play the file on my Apple TV the subtitles sometimes don't show. I have selected them in Captions, like always, but nothing. With one file only the first few lines were shown but later disappeared. Some files play without problems. I noticed if I import the mp4 files into iTunes on my macbook the same issue occurs. The file where only the first few lines of the subtitles works, stops at the exact same moment on my laptop. If i extract the subtitle from the mp4 nothing seem wrong with it. Does anyone have the same issue or a solution for this problem?