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Maybe you should be a bit more specific. When talking about a Blackmagic device, I would assume that you're talking about a capture card which takes your source signal (e.g. HDMI) and feeds this into the computer over PCIs slots or USB? You're talking about

On 8/20/2021 at 1:12 PM, Rinu said:

blackmagic ndi capture at 1080p at 30hz

We stopped using Blackmagic devices quite some years ago due to the total lack of support and the quality of their drivers. Therefore I actually can't say whether there is a Blackmagic NDI encoder/decoder on the market or not.

NDI is a signal traveling through the network, usually encoded by some hardware encoder but sometimes also encoded by the source device itself.

Trying to use video signals coming into physical inputs of a capture card and signals using NDI encoding will most probably end up in a lack of synchronization.

Encoding and decoding video signals to/from NDI usually leads to appr. 1 frame delay since the encoder has to analyze, compress and repack the incoming stream into the NDI format. When we measured the difference between signals going directly into a Datapath capture card and those from the same source going through a fast NDI converter into WATCHOUT, we measured 1 frame difference. On other servers with different capture cards we even saw that the NDI signal was a frame faster than the captured signal.

If the signal needs to be changed in the frame rate or resolution, the delay can even be noticeably longer. If you compare, you should use the same frame rate and resolution on the source side and in WATCHOUT. Then you can measure whether the capture card is faster (which is probably the case) and how much faster it is. Adding frame rate conversions or scaling will usually lead to more latency and this will be different on a capture card or the NDI encoding process.

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