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Thread: video chat and performance tuning

  1. #1
    Join Date
    Feb 2012
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    6

    Default video chat and performance tuning

    Hello,

    I'm developing a multi-party video chat application, I'm wondering if there are settings where I can have the streams degrade gracefully into lower/higher quality based on bandwidth detection or packet loss. I know the encoding quality is on the client side, can I detect frame loss either there or from the server somehow?

    Most of the documentation/examples I'm finding are geared towards other things and not live video chat.

    Just wondering for some general approaches, or links, that I can look over and review.

    Thank you.

  2. #2
    Join Date
    Dec 2007
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    21,962

    Default

    All or most of the Tutorials include section for multi-bitrate streaming:

    http://www.wowza.com/forums/content.php?4

    Wowza uses .smil file (and other methods) to arrange different bitrate versions of a stream. Each one must be key frame aligned. For vod take a look at the Expression 4 Encoder templates:
    http://www.wowza.com/forums/content....ideo-on-Demand

    For live, the best option is the Wowza Transcoder
    http://www.wowza.com/forums/content....wza-Transcoder

    Some live encoders can produce key frame aligned sets, but some can't. You can test/debug alignment by enabling a Property:
    http://www.wowza.com/forums/content....rame-alignment

    If the logs show the items are not well aligned then it won't work.

    For Flash RTMP Dynamic Streaming, the JW Player solutions works well:
    http://www.longtailvideo.com/support...amic-streaming

    This bridges server-side smil and client-side RSS for above
    http://www.wowza.com/forums/content....amic-Streaming

    Richard

  3. #3
    Join Date
    Feb 2012
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    6

    Default

    Richard,

    Thank you for your time and reply.

    My question stems from encoding on the server side. This is live chat, so we'd be using the low-livelatency stream type. I basically understand, through a combination of your links, whats required from the client side.

    On the server side, however, we'd have to use a transcoder (Wowza Transcoder AddOn?) to encode the different streams at the variable bitrates. My question is, will this conversion always be done, or only on request? Is this cpu intensive? My concern is whether or not this is resource intensive, obviously what would be ideal is if the transcoding only kicked in when the variable bitrate was requested, but I can't really find any implementation specific details on it.

    Again thank you so much for your time.

  4. #4
    Join Date
    Dec 2007
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    Default

    Actually, sorry, I was too focused on the multi-bitrate aspect of your question, because a better answer is that multi-bitrate (including using Wowza Transcoder) is probably not going to work in a chat application, because of added latency mostly, and that you are normally using very low bitrate streams in a chat application anyway.

    Richard

  5. #5
    Join Date
    Feb 2012
    Posts
    6

    Default

    Yeah, I thought that might be an issue.

    One last question: is there a stage I can detect failures, dropped frames, etc. on the publishing side, for instance if the user is limited by upstream can I get notifications of that in a server side module or on the client side and adjust the quality from there.

    Thanks again

  6. #6
    Join Date
    Dec 2007
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    21,962

    Default

    You can monitor streams, but you won't be able to adjust streams, unless you use the Wowza Transcoder. You can use this method to Transcode selectively:
    http://www.wowza.com/forums/content....erver-side-API

    Here is a stream watchdog example:
    http://www.wowza.com/forums/content....tream-Watchdog

    Richard

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