I have a custom M3U source (stream format HLS). Each channel has a WebVTT subtitle track, and every cue has a proper end time, usually 2–7 s after it starts.
In the Channels app on Apple TV and iPhone, a subtitle stays on screen until the next one replaces it. If nobody talks for a while, the last line just sits there. Easy repro: stop sending new cues and the last one stays up forever.
What I've checked:
- The same playlist in Safari clears every cue on time.
- The DVR does its part: stream.mpg has a clear ("\r") at each cue's end (e.g. text at 30.23 s, clear at 35.56 s, next line at 38.67 s). The app seems to ignore it.
- CEA-608 in the same stream clears fine on the same Apple TV. Only the WebVTT path sticks.
Expected: the subtitle goes away at the clear, like it does in Safari.
A related thing with EIA-608/708: I'd happily switch to 608 to get around this, but on Apple TV every 608/708 caption gets drawn left-aligned, even though each line is centred with PAC indents and tab offsets, as the spec allows. So right now I can choose between captions that clear but hug the left edge (608) and centred captions that never go away (WebVTT). The 608 captions also show up as a separate, unnamed "Track 2" next to the WebVTT one.
Happens on both Apple TV and iPhone.