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For example, a live GoPro video is being streamed to a HDMI capture software on Windows. The live stream of an office with the lights on has a bitrate of X and a latency of Y ms. If the lights in the office are turned off so all that is captured in the live video stream is a red light bulb and a black background, will the new bitrate be less than X? Will the new latency be less than Y ms?

The resolution is maintained throughout at 1080p at 60fps.

I'd appreciate any help you folks can be! enter image description here

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so all that is captured in the live video stream is a red light bulb and a black background

No. You can't get black background. You will get any possible type of noises, many shadows and all kinds artifacts of camera's matrix.

will the new bitrate be less than X?

  • No. As GoPro writes constant bitrate (CBR)
  • No. As new noises can require even more bitrate than static image.
  • Yes, if you will fill background with black color in video editing software and select non-CBR mode for compression

Will the new latency be less than Y ms?

No. Delay causes by some buffers. Buffers for N frames, buffers for N bytes. If you lower bitrate, you can INCREASE delay in some cases (actually, it's true to very low bitrates).

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Like much with technology (and life), it depends. You didn't specify what software, protocol, or codec you are streaming with, so there are quite a few variables.

Will the bit rate drop?

If you are using a constant bit rate (CBR) codec, no it will not. As the name implies, the bit rate is always the same regardless of the content.

If you are using a variable bit rate (VBR) codec, it might be lower than when the lights are on. It may also not be significantly lower, because, as the other answer alluded to, you will get a lot of noise. When the light level drops, the camera will automatically increase the gain which will result in color artifacts in the dark area, like in the sample video below. It is very difficult for codecs to handle noise, so you might actually see an increase in the bit rate over a brightly lit scene with little movement.

Will the latency drop?

If you are using a codec that has several latency modes, then the it might. However, most of those codecs are commercial products that are either a proprietary codec or fudge things in incompatible ways within the standard. That makes it unlikely that you are using one of those codecs. On top of that, those codecs usually make you select the latency mode before starting the stream and it is then fixed while the stream is up.

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