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Time misalignment on PHDS streams, when seeking forward / back on an OSMF player with subtitles

Jul 30, 2012 3:12 AM

Tags: #sync #time #player #osmf #stream #captions #subtitles #closed #current #seek #phds #mis-alignment

We are using PHDS streams with an OSMF based player.


all streams that are received via RTMP have no problem

with our player in regarding to showing the subtitles (closed captions)

in sync.


yet when we get the stream via PHDS it seems that once in

a seek or two, the captions (subtitles) shift ahead for about 0.5-1 secs.


and as mentioned another seek can fix it or leave it out of sync.


our conclusion is that it has to do with the FMS serving the

stream which somehow deviates the current time of the stream.



ps: when getting the stream for the same video via RTMP

via the same player - the subtitles are OK, the problem is only PHDS



any ideas?


  • Currently Being Moderated
    Jul 30, 2012 7:02 AM   in reply to Syberkitten

    Can you tell me which FMS build you are using and what file you are using? Especially codec details and how closed captioning data is present in the file, is it present in the Video data or as a separate track in Data messages.

    Does HDS unencrypted plays fine with closed captions?

    I need this information to understand your workflow clearly which can help me to diagnose the problem better.

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  • Currently Being Moderated
    Jul 31, 2012 6:35 AM   in reply to Syberkitten

    This is expected.


    In case of RTMP you are not observing this because RTMP seek is fast as the server sends some data immediately when we seek irrespective of the keyframe and the player starts playing it so it is in sync.


    But in case of HDS we have fragments which are downloaded by the player and it has keyframes in it which can be positioned anywhere in the fragment. So, when you seek you get the current time but this might not be same with the time when the player actually starts playing the fragment as it looks for the keyframe. So, sometimes it can be the case that it got the keyframe immediately when it seeked but tsometimes not.

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  • Currently Being Moderated
    Sep 24, 2013 11:37 AM   in reply to Syberkitten

    What extension was the closed captions for HDS? Have you done CC for HLS?

    . I am trying to implement cc for both streaming ?


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