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Thread: Methods for syncing mixer audio with single/multiple NDI feeds?

  1. #1
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    Methods for syncing mixer audio with single/multiple NDI feeds?

    I'm new to NDI and have found that my single NDI camera has feed latency between 200-500ms.
    I think it is varying due to initial LAN switch and camera power-up.

    Aside from manually adjusting for this (I'm using OBS Studio on Win10), are there any tried and true methods for "calibrating" for this?

    I'm curious to know other handle this as more NDI feeds are added (if it impacts at all)? I suspect each feed would need separate tuning.

    Do you leave the camera (PoE LAN switch) always on to avoid dealing with it? What about after a power loss?

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    Quote Originally Posted by chulester View Post
    I'm new to NDI and have found that my single NDI camera has feed latency between 200-500ms.
    I think it is varying due to initial LAN switch and camera power-up.

    Aside from manually adjusting for this (I'm using OBS Studio on Win10), are there any tried and true methods for "calibrating" for this?

    I'm curious to know other handle this as more NDI feeds are added (if it impacts at all)? I suspect each feed would need separate tuning.

    Do you leave the camera (PoE LAN switch) always on to avoid dealing with it? What about after a power loss?

    500mSecs sounds like way too much, and probably indicates a lower level problem.

    Our experience shows that in cases where video stream bandwidth exceeds available network bandwidth, you will of course drop frames, but we also see an increase in latency of several hundred milliseconds - which would seem to correspond with your report.

    So - I suggest you take a closer look at your network infrastructure - and try to eliminate your entire existing network for a control test.

    To answer your specific question - if there is a genuine need to adjust sync between cameras - the Sienna NDI Processing Engine includes a sync delay module which can be used across unlimited feeds to delay audio and video, and to adjust lip-sync on each stream.
    http://www.sienna-tv.com/ndi/ndiprocessor.html

  3. #3
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    Quote Originally Posted by livepad View Post
    500mSecs sounds like way too much, and probably indicates a lower level problem.

    Our experience shows that in cases where video stream bandwidth exceeds available network bandwidth, you will of course drop frames, but we also see an increase in latency of several hundred milliseconds - which would seem to correspond with your report.

    So - I suggest you take a closer look at your network infrastructure - and try to eliminate your entire existing network for a control test.

    To answer your specific question - if there is a genuine need to adjust sync between cameras - the Sienna NDI Processing Engine includes a sync delay module which can be used across unlimited feeds to delay audio and video, and to adjust lip-sync on each stream.
    http://www.sienna-tv.com/ndi/ndiprocessor.html
    500ms may be extreme and it's possible my 400ms audio delay was even on the high side of what was needed (lip-sync based on lip-reading with audio). I'm curious how Sienna accomplishes this or is it just a user input for delay in milliseconds like OBS has and it's up to the user to determine the delay? Is there any sort of audio-visualization / sync-calibration standard to precisely determine the needed delay?

    Is there a tried and true method for a controlled bandwidth test? Our network consists of a single NDI camera (with plans to add more) on a Gigabit PoE switch (both brand new) connected to our Spectrum router (relatively new and Gigabit) and using a brand new custom built power PC (also Gigabit).

    With an NDI camera alone on a closed network, how much would you expect latency to vary and how much would regular power cycling of the network equipment contribute to that variance post-boot (if any)?

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    Just an FYI, there are youtube videos that are just synced audio pulses with video movement that are very handy for dialing in a good sync. Just search audio sync test on youtube. Youtube sync is pretty much always good enough for most uses. You can point your camera at a phone playing the video. If that isn't good enough there are probably some pretty good apps, though I don't bother and just use youtube.

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