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Thread: Fast channel Switching delay

  1. #1

    Default Fast channel Switching delay

    Hi,
    I need to implement a live streaming solution with wowza, DRM manager and HLS stack player for android.
    I am asking on how much the fast channel switching delay can be for the final user when changing the live channel.
    How to optimize it ? any wowza config parameters to set (streams provided to wowza by ffmpeg) ?

    thanks,

  2. #2
    Join Date
    Sep 2011
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    1,931

    Default

    Hi,
    The stream delay for HTTP clients can be reduced by altering the chunk duration to make it smaller. As chunks are created on keyframes, a frequent keyframe interval is required (equal to or less than the chunk duration).
    The keyframe frequency will be set at the encoder so in this case that would be FFmpeg. For altering, please see the Apple HLS packetization article.

    When using Adaptive bitrate (ABR) streaming, the client will request a different playlist for the new chunks while playing the chunks from the current playlist making the switch seamless when the streams are keyframe aligned.

    Regards,
    Jason

  3. #3

    Default

    Hi,
    thank you.
    And what if using Wowza Transcoder AddOn ?
    Do you have an idea about the delay, en seconds, for HD and SD quality ?

  4. #4
    Join Date
    Jun 2011
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    1,037

    Default

    Hi,
    It is hard to say. The Transcoder AddOn will likely add only a few hundred milliseconds of delay. It will largely depend on the hardware being used and whether cpu or gpu encoding is being employed.
    But even for HD the delay is still only measured in hundreds of milliseconds.

    Daren

  5. #5
    Join Date
    Sep 2011
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    1,931

    Default

    Hi,
    The same can also be said in the fact that the client will be playing a HLS chunk when it requests the new chunks at a different bitrate which means you will have downloaded the chunk before playing it as with any other ABR stream.
    When the streams are keyframe aligned (from our transcoder or another source) the switch itself should still be seamless (no delay when switching).

    Jason

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