H.264 and H.265 are the dominant codecs in use for IP based video. The newer variant H.265 (HEVC) uses approx 70% less bandwidth at all resolutions.
Frames Per Second
H.264 capable cameras and encoders are very common in existing deployments, H.265 are less common but most new devices support this codec.
Codec choice is not the only factor affecting the bandwidth requirements, we also have to consider the client’s choice of Bit Rate control.
VBR, MBR or CBR?
When configuring IP Video devices you are provided a choice between three bit rate modes. For a deep dive on this topic, I recommend reading this guide from the team at IPVM.
From that guide…
"Constant vs Variable vs Max Bit Rates (CBR vs VBR vs MBR)
The amount of bandwidth a camera needs at any given time to maintain a specific quality level varies over time, sometimes substantially. For example, a camera might need 1Mb/s for an empty school hallway on a Sunday afternoon but might need 4Mb/s for that same spot come Monday morning."
Why? Because video compression codecs like H.265 minimize the bandwidth required by only sending video data for areas of the image that are changing. An empty hallway has minimal visual changes so the bitrate is low. If it’s full of walking students that will inevitably increase.
Here’s a breakdown of each mode;
Variable bit rate (VBR): The bit rate changes to keep compression at a set level regardless of activity.
Maximum bit rate (MBR): aka VBR with a cap. The bit rate changes but no more than a user-defined maximum.
Constant bit rate (CBR): The bit rate of the camera does not change even if the scene does.
So we use VBR right? That is most the most efficient mode? Not if there’s a requirement for the cameras to be used at night or in low light. Due to peculiarities with how night vision images are handled by these codecs, that empty hallway using 1.1Mbits/s bit rate would explode to 10Mbits/s or more in night vision mode. We don’t want that, which is why most deployments follow the industry standard and use MBR as the bit rate mode. Again, the IPVM guide goes into this in more detail if required.
When assessing the bandwidth requirements for an IP video deployment we need to know;
What codecs are in use?
What bit rate mode is used?
What data do you have on bitrate required by existing cameras in your network (if available)?
In short, the answer to the question “How much bandwidth is needed?” is “It depends.” If you need to explore the various options for each codec this tool from JVSG is the best I have found so far.
In the next article in the collection, we explain how Celona's unique MicroSlicing technology can be configured to guarantee specific latency and throughput metrics on CBRS LTE for video traffic flows.