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NDI Black frames in vMix


I'm dealing with a problem that vMix support team and PTZ Optics support team doesn't have a solution for it yet :(

They heard about it but they don't know why this happens.

In few words, I will describe my problem.

From time to time, in vMix, I have couple of black frames from my NDI cameras (PTZ OPTICS 12x). They don't have a pattern, they just appear and ruin my recording.

What I discovered since I have this problem and trying different stuff:

Camera web interface settings:

I have black frames when I use Encode Protocol H264.

I have grey frames when I use Encode Protocol H265.

I didn't test the MJPEG very much because of the big lag.

If I rise the bitrate to the maximum - 20480kbps, I have more often  those black frames.

If I lower the bitrate to 12000kbps (NDI HIGH PROFILE), I still have those black frames, but less often.

Once,  I didn't have any black frames at all on one camera, but I had on the other one. I checked the settings and I discovered that the "good" camera, had 4000kbps bitrate. 

I have gigabit network, I don't think that a 40000kbps (from 2 cameras) bitrate should be a problem at all. The cameras are powered through the network cable from a TP LINK POE SWITCH with 5 ports.

I attached a photo with my network monitor. When the black frames appear, I can see a spike on the network like the one in the picture.

Maybe I can tune some settings from the camera menu to get rid of that black frames but I don't know the meaning of them. Maybe you can help me.

Fluctuate Level, Slice Split Enable, Split Mode, Slice size.

I do recordings more often then streaming, so I need the highest bit rate because it matters in my productions. If the cameras are working without black frames at's too low for me. I need every bit of quality than I can get.

Based on my informations, maybe someone can see a solution...

Thanks for your help.

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