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Thread: NDI - Visual Artefacts

  1. #1
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    NDI - Visual Artefacts

    Hello everyone!

    This is more or less a copy-paste of a reddit post I made. Hopefully someone here will be able to shed some light.

    I'm attempting to use NDI to send a capture of a computer game from one computer to another. The computer running a game is using OBS with the OBS-NDI plugin (I've also attempted to use NDI Scan Converter with the same result). The scene and output resolution match each other, and have been tested at 3840x2160 and 1920x1080, both at 60 FPS. NDI is used in non-low bandwidth mode. The gaming computer is connected to a networking switch over 40 Gbps. The receiving computer is also connected over 40 Gbps. They're in close proximity to each other with a couple of hundred microseconds of latency at most, within the same subnet. The highest bitrate that I've seen using a feed that is virtually impossible to efficiently compress (random colored noise, high entropy) was around 380 Mbps.

    Regardless if the NDI output is received and viewed locally on the "gaming" computer, or on the receiving computer over the network, very noticeable compression artefacts can be seen, both banding and microblocking. This is an issue I've had with NDI since I started testing it about a year and a half ago. Despite searching around, it seems there hasn't been a lot of research into what NDI actually does to the source, visually.

    If someone is sitting on more knowledge than readily available, perhaps a way to force NDI to not be so aggressive on saving bitrate, do tell.

    I can add some images to show the issue. If the interest is here, I can put several of them in an archive and upload to a file service.

  2. #2
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    Here are two pictures to show the issue. The first one is directly from the source, and the second one is over NDI. The full resolution is 3840x2160. I've uploaded them according to imgur's guidelines to make sure they don't lossily compress the images, so they're losslessly compressed as PNG files.

    Source

    NDI

  3. #3
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    Quote Originally Posted by Jent View Post
    Here are two pictures to show the issue. The first one is directly from the source, and the second one is over NDI. The full resolution is 3840x2160. I've uploaded them according to imgur's guidelines to make sure they don't lossily compress the images, so they're losslessly compressed as PNG files.

    Source

    NDI
    Its likely the majority of the artefacts in your example are due to 8-bit encoding. Somewhere along the line with NDI 4.0 you will be able to do this with 10 or 16-bit encoding and the artefacts in the smooth graduations of the picture would likely be better replicated. There does appear to be a small color space change too which may be something else, for example related to a change between RGB and YUV colorspaces.

    just my 2c.

  4. #4
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    Quote Originally Posted by livepad View Post
    Its likely the majority of the artefacts in your example are due to 8-bit encoding. Somewhere along the line with NDI 4.0 you will be able to do this with 10 or 16-bit encoding and the artefacts in the smooth graduations of the picture would likely be better replicated. There does appear to be a small color space change too which may be something else, for example related to a change between RGB and YUV colorspaces.

    just my 2c.
    Thanks for adding to the discussion!

    A higher bit depth can definitely help with both banding and "mosquito noise". However, 4.0 seems to have been slated for Q2 this year, which has passed, and I cannot seem to find a new date.

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