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Thread: Help to determine terms in nDVR study

  1. #1

    Default Help to determine terms in nDVR study


    I feel confused with some terms in nDVR study. Please help me to clarify that:

    1. chunk : the chunk seems to be the collect of one m4fa + one m4fv (+ m4fv) from here, there are many chunks in single directory. But what's the relation of chunk length and key frame interval?
    2. DVR store : nDVR-Playlist-Request-API talks about live DVR store and recorded DVR store, can you please help to explain more about the live/recorded DVR store ? I do not really understand why there are 2 type DVR store sourced from the same upstream.
    3. playlist that request live/recorded stream : The HLS player always use URL like 'http://[ wowza-address ]:1935/dvr/myStream/playlist.m3u8?DVR' to get the upstream recorded file list, it seems no parameter to ask the stream type like live or recorded but nDVR-Playlist-Request-API talks about live/recorded stream. How to control that by player?
    4. definition of live/recorded stream : same nDVR-Playlist-Request-API -- "If the stream is being recorded it is considered live, otherwise it is considered recorded". what it means that 'stream is being recorded'? does it means the upstream stopped?

    Please help to correct that if some of my concept are wrong... thanks

    Last edited by spiritsoul; 07-16-2013 at 02:53 AM.

  2. #2


    Hi there,

    1] nDVR breaks chunks on keyframes. This is useful for adaptive bitrate switching where key-frame-alignment is mandatory

    For more information on chunk duration and advanced configuration of nDVR, see this article:
    How to plan your Wowza nDVR workflow

    2] There are not 2 dvr stores. They are talked about in different ways, depending on live or not. But there is just one store.

    3] If it is a live stream it will play from the live point, if you use the url of http://[ wowza-address ]:1935/dvr/myStream/playlist.m3u8?DVR you are playing a live stream. You can specify a specific duration and start time of a stream by using dvrPlaylistRequestDelegate,

    This url will play the stream from minute 1 through minute 6.

    4] nDVR is always recording, when a stream is actually "live" Wowza plays from the live point, but is still recording so the user can pause or seek backwards. When the stream is not live, the recording is used and starts from the beginning.


  3. #3



    Please correct my understanding if any problem.
    One chunk represents n * (data of one keyframe + data in key frame interval). The dvrChunkDurationMinimum property decides chunk minimum duration so it decides the n. Fixed duration does not mean fixed size because each (data of one keyframe + data in key frame interval) size is possible varying. Therefore the chunk size is varying in fixed dvrChunkDurationMinimum property.

    If there is a stream named myStream it was disconnected and then restarted, and it continues to send upstream to Wowza, it is a live stream.
    so myStream includes at least 2 stores right now, first is in [install-dir]/dvr/[applicationname]/myStream.0 , this is a 'recorded DVR store' , the second named myStream.1 and it is a 'live DVR store' if the live point is written into the myStream.1
    If HLS player wants to play from the live point, uses
    and it delays 3 chunks
    If player wants to play a specific duration that crosses myStream.0 and myStream.1 , that also can be achieved by using dvrPlaylistRequestDelegate like
    . What Wowza needs is to add dvrPlaylistRequestDelegate properties to Application/DVR/Properties
    and it's optional to customize the getDvrPlaylistRequest methods

    If there is a stream named myStream2 it was disconnected, restarted and then disconnected again, it is a recorded stream.
    In this case both the myStream2.0 and myStream2.1 are recorded DVR stores

    Last edited by spiritsoul; 07-16-2013 at 08:17 PM.

  4. #4
    Join Date
    Dec 2007


    There is just one store. myStream2.0 and myStream2.1 are part of the same store, not different stores. The terminology "live" vs "recorded" store is about whether the stream is live at that moment or not. But there are not two stores per nDVR stream, just one. This may be confusing, which is something I will forward to Documentation. In any case, there is just one set of chunks, albeit in these different folders, for each nDVR stream.

    nDVR chunks have to be broken on key frames. dvrChunkDurationMinimum is a minimum: "dvrChunkDurationMinimum controls minimum nDVR chunk size, in milliseconds (ms). The default value is 1500 ms. Chunks will still be broken on key frames."


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