Hi there,
After updated to HLS V4, we found two problems in iOS devices with our WebVTT format subtitles:
1) iOS11.4.1 subtitles display does not sync with audios (some devices are ok, some are not)
2) iOS12 subtitles donot display or diappear afer playbakc for a while. (most of our devices with iOS12 have this problem)
the WebVTT as follows:
--------------------start sample-------------------------------
00:00:00.000 --> 00:00:07.978 line:80% position:20%
-Du likner pa en mus.
00:00:00.000 --> 00:00:07.978 line:84% position:12%
-Det er fordi jeg er en mus.
00:00:07.978 --> 00:00:10.000 line:84% position:12%
Det er i dag! Det er i dag!
X-TIMESTAMP-MAP=MPEGTS:1251267422,LOCAL:00:00:00.000
00:00:00.000 --> 00:00:01.618 line:84% position:12%
Det er i dag! Det er i dag!
00:00:02.618 --> 00:00:05.498 line:84% position:30%
Det er i dag!
00:00:07.018 --> 00:00:09.338 line:84% position:30%
Det er i dag!
00:00:09.498 --> 00:00:10.000 line:80% position:7%
-I dag er alltid i dag, George.
00:00:09.498 --> 00:00:10.000 line:84% position:15%
-Kan jeg ikke fa bli med?
-------------------end sample--------------------------------
we tested the follwoing sample flow is OK:
http://sample.vodobox.com/planete_interdite/planete_interdite_alternate.m3u8