Great report! Can you elaborate on the impact of altering P frame interval (or some say, I frame interval or keyframe interval)? Is there any significant relationship between keyframe interval and quantization? Clearly the shorter the time between P frames, the higher the bandwidth but what are the other impacts on the video? It's another opportunity for confusion on which way the scale goes and its impact on quality and bandwidth. Thanks!
In general, P and I frames don't directly impact quantization levels. They will impact the visual artifacts in video, though. So when I-frame interval is long, you'll see trails form behind moving objects, and additional noise throughout the image until the next I-frame. Conversely, when I-frames are close, you'll see less of this issue, but there is generally not much of a practical improvement from intervals shorter than a second.
You've used the term "artifacting" - but it looks more like motion blur. Did you have the shutter speed at default (usually 1/30 or 1/60 sec)? This is probably not a fast enough shutter speed to stop motion blur - even in this scenario.
By the way - really enjoy reading your reviews, commentary on the industry, etc. - keep up the good work.
- bitrate control( how well does it handle changes)
Quantization parameters is a small part of the overall equation, and making some conclusions based on it is likely misleading.
If I would explore how advanced codecs are from different vendors, I would analyze other parameters as well: so you can see that this vendor uses macroblocks of such type, motion vectors of such accuracy etc... I know nobody would be interested in reading:-)
But only real criteria of image quality/bitrate is subjective "I like it more" or "I like it less", not quantization by itself.
Thank you for another great report IPVM. Question, how did you measure image quality? Did you use some type of tool or did you just manually review the video? Also what tool did you use to watch the video? The viewer inside the camera, another third party tool (ie- VMS)? These details can affect the perceived quality, hence I'm asking. Thanks!!!
If you mean image quality as in visible image quality, we visually compare cameras. There are software tools that measure "image quality", but I would not trust software measurements to determine what is or is not a usable image.
We view video multiple ways. Practically every cameras in this test was viewed using Exacq, VLC Player, and the camera's web interface. We don't rely on just one, but that being said, rarely are there practical differences between one VMS and another or between the web interface and a VMS, etc.