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Thread: bad frames when crossing network segments

  1. #1
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    bad frames when crossing network segments

    When I send (via unicast) frames from a virtual machine and receive those frames on a workstation in a different segment, it appears as if a significant number of frames are missing. The video looks choppy and it stops before it reaches the end.

    Also noteworthy is that I get an error when I attempt to run Studio Manager on the VM. It fails because the GPU does not support shaders. Could this be related to the issue with the frames? My application does run and generate NDI frames on the VM. The issue is the apparent stuttering.

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    Quote Originally Posted by jgeduldig View Post
    When I send (via unicast) frames from a virtual machine and receive those frames on a workstation in a different segment, it appears as if a significant number of frames are missing. The video looks choppy and it stops before it reaches the end.

    Also noteworthy is that I get an error when I attempt to run Studio Manager on the VM. It fails because the GPU does not support shaders. Could this be related to the issue with the frames? My application does run and generate NDI frames on the VM. The issue is the apparent stuttering.
    If you are losing frames when using unicast this is likely to be network packet loss. You may want to force TCP connectivity instead with NDI Access.

    StudioManager on VM will fail where the Virtual Environment is not delivering the level of DirectX or OpenGL required. This is normal for NewTek Studio Manager. Other NDI Viewing apps which dont need those GPU services will work fine on VMs, and it has nothing to do with the first question about lost frames.

  3. #3
    Registered User roddyp's Avatar
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    Quote Originally Posted by livepad View Post
    If you are losing frames when using unicast this is likely to be network packet loss. You may want to force TCP connectivity instead with NDI Access.
    Is that possible - I thought NDI used UDP regardless, and there's no visible TCP option in Access Manager - Is this a V4 thing?

  4. #4
    Quote Originally Posted by roddyp View Post
    Is that possible - I thought NDI used UDP regardless, and there's no visible TCP option in Access Manager - Is this a V4 thing?
    NDI 1.0 thru 3.0 used TCP. NDI 3.5 thru 3.8 uses UDP and will fall back if to TCP when working with older clients. NDI 4.0 (not released yet) will give you the option to choose UDP or Multi-TCP receiving on a per client basis. NDI 4.0 will default to Multi-TCP.
    Kane Peterson
    Solutions Architect
    NewTek, Inc.

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    My frames are 720p.
    Is each UDP packet one compressed frame?
    About how many bytes in a UDP packet?
    Last edited by jgeduldig; 09-09-2019 at 02:40 PM.

  6. #6
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    Quote Originally Posted by jgeduldig View Post
    My frames are 720p.
    Is each UDP packet one compressed frame?
    About how many bytes in a UDP packet?
    Each frame will require many UDP packets, which are typically around 1500 bytes each or less.

    However, if you lost a packet, you probably lost the entire frame, unless you have FEC (forward error correction) where the sender is effectively pushing some redundancy to deal with lost packets. My understanding is that NDI does use FEC in some configurations, so if you are still losing frames, it may be that you are losing so many packets that the FEC can't compensate.

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