Optimizing Bandwidth Consumption Through I Frame Settings

By John Honovich, Published Feb 03, 2010, 07:00pm EST

A blog post from Genetec offers an interesting example of lower level IP camera optimizations that can impact bandwidth utilization. Genetec claims such an optimization can lower bandwidth consumption by 2 to 3x.

The basic point is that some VMS systems allow you to adjust how frequently a full image is sent in a MPEG4 or H.264 stream while others have a fixed setting. By making the interval longer, you can reduce bandwidth consumption because the encoder/camera is just sending small updates rather than the whole picture.

Genetec's point is that they allow this optimization while many VMS systems do not (which we believe is generally true though we have not verified this systematically).

In the comments, the concern we expressed was that lowering the I frame rate can cause quality problems. If too much of the scene changes (a moving PTZ, a crowded area), the quality of the video can suffer significantly. Genetec responded that the MPEG-4/H.264 standards allow cameras to dynamically increase the I frame rate beyond the setting if needed. Genetec reports that many cameras implement in this fashion. On the other hand, we have seen some cameras in the field that lock on the set I frame rate causing video quality problems when scene complexity is high.

On a higher level, the variance between stream settings on the camera and settings available are an important point. We even see this at a more basic level where cameras might support VBR and CBR but the VMS only supports one of the two (potentially creating problems, or at least, inefficiencies).

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