IPVMU Certified | 12/31/14 01:24pm
I guess in a sense it's a weakness because with CBR or VBR/w'cap, you can estimate the maximum storage you might need, but the end result might be that you needed less that you thought and bought more storage than you needed.
Some people including engineers prefer situations that are precisely deterministic, even at the expense of being "worse". For those folks, an improvement that reduces certainty is a defict. That psychology may be at work here.
I have not ever seen a switch that will not handle H.264, althought this is an anecdote and others may have a different experience.
Why would losing an I-frame be a big problem? There is always a "next" Iframe to restart with.
My biggest issue the difficulty of stepping backwards frame by frame during forensic review. It can be done but it's quite computation intensive. Motion-JPEG makes this much easier.
In general, any temporal compression introduces a new class of artifacts and H.264 does not escape this problem. That said, most cameras have several dimensions of control of the encoding process and, if the default settings are not acceptable, some compromise can be found.
IPVMU Certified | 12/31/14 03:09pm
"Temporal Compression" can you explain that? I know what temporal means but I don't understand your context.
What are the new class of artifacts for H.264? You lost me on this one as well.
Sure, John. Standard compression like Jpeg takes place seperately on each frame and there is no dependency on preceding frames - that is, no time component.
H.264 (and others) add a second major compression method where frames sent are dependent on preceding (an even future) frames. This is a time based dependency since these frames are a time based sequence. Thus, the "temporal" terminology.
This generally means that only changes in content between frames need to be transmitted. The display tool "adds up" these changes to deliver a complete and updated image for each frame. Because errors happen, all real systems deliver a complete frame (called an iFrame) every so often to serve as a clean restart in case some of these changes got lost.
A full discussion of this topic is beyond my teleprompter script :) but hopefully this helps.
Further, Jpg compression is optimized for continuous tone images. A fairly well-know artifact (for example) of Jpg is it a sort of white blurring on any sharp edges depicted in the image. This is also present in H.264.
H.264 deals with changes across successive frames with additional compression based on motion prediction and other statistical methods. This tends to add motion blur artifacts that are not present in a Motion-JPG stream captured with a fast shutter.