Subscriber Discussion

H.264 Compression Questions?

Undisclosed Integrator #1
Mar 14, 2013

Wanted to just clarify something about H.264 compression:

If using example a 2mp camera with H.264 compression, as we all know the minimum bandwidth required for the 2MP camera is about 2.0MB to 4.5MB depends the frame rates per camera set and the activity of the image.

My question, if I have a 2mp camera which there is no motion at all, or the activity motion will various from 10% to 90% of the image size, do we still require to have a minimum of 2.0MB of upload per camera, irrelevant how big is the image size being on motion.

Brian Karas
Mar 14, 2013
Pelican Zero

Karim -

The answer varies, and will depend somewhat on the quality of the sensor and the ISP behind it. Even in a scene with "no motion", there can be apparant motion for example if the sensor produces a "noisy" image, or if the scene lighting is not even and similar factors. For bandwidth budgeting purposes I would assume 2Mbps as the absolute minimum in all cases (and personally, I think that's even a little low), in very very rare cases you may be surprised to learn that with a very clean indoor scene, low fps, and high compression you can get by with only 1.5Mbps, but that is going to be a very rare exception case.

Karim Cassar
Mar 14, 2013

thanks so much for your information Brian.

John Honovich
Mar 14, 2013

Karim, it depends first if you are using CBR or VBR. If you are using CBR, then you probably need to go 2Mb/s or 4Mb/s to be safe for times when motion is greater. However, with VBR, 2MP cameras, even at full frame rate will routinely go less than 2Mb/s.

Also, 2Mb/s or 4Mb/s is really for 30fps (or at least 15fps+).

I strongly recommend to use VBR with a cap and let the camera automatically adjust to the scene conditions.

Carl Lindgren
Mar 14, 2013

Keeping in mind that at least one manufacturer's CBR is actually VBR with a cap (aka Constrained Bit Rate).

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