Hello,
I'm trying to understand what will be the correct way to signal X-TIMESTAMP-MAP in live streams.
For VoD (e.g. manifests with EXT-X-ENDLIST), I found to currect way to use a constant local/PTS pair, where the PTS is the the PTS of the IDR of the first segment)
So this mode is working properly and video/subtitles are synched:
frag1:
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:284722
00:00:36.849 --> 00:00:39.729
-Mina herrar.
-Mr Turner!
00:00:39.889 --> 00:00:43.769
Min far och jag beundrar
detta himmelska verk.frag2:
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:284722
00:00:39.889 --> 00:00:43.769
Min far och jag beundrar
detta himmelska verk.
00:00:43.929 --> 00:00:49.689
Minns jag rätt: hade vi lyckan att få
se det på utställningen förra året?frag3:
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:284722
00:00:43.929 --> 00:00:49.689
Minns jag rätt: hade vi lyckan att få
se det på utställningen förra året?However for live it is impossible to rely on a "first" PTS, so I tried the following, which doesn't seem to work:
frag1:
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:36.000,MPEGTS:3524722
00:00:36.849 --> 00:00:39.729
-Mina herrar.
-Mr Turner!
00:00:39.889 --> 00:00:43.769
Min far och jag beundrar
detta himmelska verk.frag2:
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:40.000,MPEGTS:3884722
00:00:39.889 --> 00:00:43.769
Min far och jag beundrar
detta himmelska verk.
00:00:43.929 --> 00:00:49.689
Minns jag rätt: hade vi lyckan att få
se det på utställningen förra året?frag3:
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:44.000,MPEGTS:4244722
00:00:43.929 --> 00:00:49.689
Minns jag rätt: hade vi lyckan att få
se det på utställningen förra året?As you can see the timing is still the same, and LOCAL and MPEGTS keep progressing relativly, but the result is subtitles out of sync.
Can you explain what is the currect behavior of X-TIMESTAMP-MAP (LOCAL vs MPEGTS), especially in live use-case?
(Tests were performed on iPhone native player, iOS 10.1.1).
Thank you
