Comments on IP Security Solutions: Omnicast requires less bandwidth than some competi...

Hi Jo, I have seen it in a number of cameras and ...

2010-02-04T00:32:44.845-05:00

Hi Jo,

I have seen it in a number of cameras and encoders. Lowering the i frame rate often causes significant macroblocking/artifacting. I agree it depends on implementation and have not tested this specifically. However, from field deployments, I have seen this issue. As an example, we had a PTZ with significant quality problems every time it was panned. By increasing the i frame rate (from 1 per to second to 5 per second), the issue went away. It seemed from the visual results that the encoder was fixed at the i frame rate and would not go beyond what was set.

Beyond that, the whole premise of changing a configuration setting to reduce bandwidth consumption by 2-3x without any tradeoffs sounds 'too good to be true'. My example above is one practical issue I have seen with variances to such a setting.

This is definitely an interesting topic.

Hi John, I have never noticed a quality difference...

2010-02-03T06:22:10.589-05:00

Hi John,
I have never noticed a quality differences during my test with fix and mobile H.264 cameras.

Nothing in the MPEG-4/H.264 standard prevent the encoder to use I-Macroblocks instead of P-Macroblocks when there's a lot of motion, I have seen it in many implementations. That's why the bitrate increase a lot when you move a dome.

Do you have specific camera manufacturers in mind when you mentionned a loss of quality?

Using some MPEG-4 domes, I observed situations where the dome only send 26 to 28 FPS at 4CIF when the I-Frame interval is set to 1 seconds (GOP Size 30) versus 30 FPS at 4CIF with a I-Frame interval >= 4 seconds.

Hi Jo, Reductions in bandwidth from I frame settin...

2010-01-30T12:24:15.536-05:00

Hi Jo, Reductions in bandwidth from I frame settings make sense. However, the risk of generating more infrequent I frames is a loss of quality, especially during times of complex movement (a panning PTZ is a worse case scenario).

I think it's valuable that Genetec supports I-frame setting adjustment, however I question whether your lower bandwidth consumption is not at the expense of lower video quality (especially during periods of high motion). This will depend on what the camera is viewing but I think this is a real and important risk (and potential tradeoff).

Thoughts?