Interesting, I tried to get them to change the word "constant" to the proper "constrained" for 6 years with no luck.
Axis Fixes VBR / CBR Setting
Published Feb 23, 2015 05:00 AM
Bit rate control is an important element in transmitting surveillance video. The three most common options as explained in our CBR vs VBR: Surveillance Streaming Guide are:
- VBR - variable bit rate
- CBR - constant bit rate
- VBR with a cap - variable bit rate with a maximum bit rate level
Historically, Axis settings here have been misleading. Now, new firmware (5.60) has fixed this. In this note, we explain what changes they have made and what this means.
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Comments (12)
U
Undisclosed #1
Feb 23, 2015lc
ling chen
Feb 23, 2015Thanks Ethan, for sharing the information.
it seems there are two VBRs ?
1. VBR no Rmax cap
2. VBR with Rmax cap
No CBR setting?
-Ling
JH
John Honovich
Feb 23, 2015Axis does not support traditional CBR, e.g., set the bitrate to 5Mb/s regardless of what the scene, resolution, frame rate, compression, etc. is.
That makes sense to me, given that maximum is simply better than constant.
lc
ling chen
Feb 23, 2015Thanks John. For big Metro and Enterprise applications, the MBR (VBR + CAP) rate control is essential.
JH
John Honovich
Feb 23, 2015Btw, I think MBR would be a good term to adopt. A 3 letter acronym makes it a clearer contrast to VBR and CBR. CBR is constant, VBR varies and MBR varies to a maximum bit rate.
BS
Brad Silvernail
Feb 24, 2015The old CBR settings were critical to manage "runaway" bandwidths with some network cameras at night. I think IPVM did one of the first studies on this and validated what we've observed for years. A 720P or 1080P camera that could manage on 2 to 4 Mbps during the day, could drive 10 to 15 Mbps bandwidth at night. The CBR settings, effecting a cap at say 5 mbps, with priority on quality, should really be a default. Thanks for the info. Hadn't seen this in the new firmware yet.
JH
John Honovich
Feb 24, 2015Brad, yes, and here is the most recent test report showing runaway night bandwidth: Tested: Lowering Bandwidth at Night is Good
Note, the new setting works the same, it just now is clearer and stops people from believing that Axis has a true CBR, which did not have previously either, despite labelling it constant.
U
Undisclosed #2
Feb 24, 2015After years of this confusing verbiage, Axis changed the language used in camera setup in firmware 5.60 (.pdf release notes), from "constant" to "maximum" bit rate, seen here:
I am unable to find the mention of that verbiage change in the release notes you linked, nor in the detailed notes of either of the 5.60.x firmware releases for the P3364.
How did you discover it?
Curiously, in the 5.60.1 notes mention is made of a change in the behavior of CBR:
Improved Constant Bitrate Control, the Constant Bit Rate (CBR) will now adjust to target bit rate quicker.
What does that mean, if 'constant' now equals 'maximum'?
JH
John Honovich
Feb 24, 2015I found alluded to in the Axis Latency whitepaper, which the spider picked up.
U
Undisclosed #2
Feb 25, 2015Wow, they are a bit conflused about this change. The paragraphs below are duplicated word for word in this manual, except for changing Constant to Maximum.
UM
Undisclosed Manufacturer #3
Feb 26, 2015I heard previously from a sytem integrator that Axis' 'CBR' (VBR with a limit) was good at limiting bandwidth, however the SI was not so happy when his customer complained that they lost frames in the recordings of an incident. Turns out that to maintain the bandwidth limit, the codec was dropping frames. This is Ok if you know what's going on but the customer was surprised and complained that his requirement of x fps was not maintained. In some applications a specified fps (or minimum fps) is a legal requirement in Europe. Is that also the case in the US?
JH
John Honovich
Feb 26, 2015"I heard previously from a system integrator that Axis' 'CBR' (VBR with a limit) was good at limiting bandwidth, however the SI was not so happy when his customer complained that they lost frames in the recordings of an incident."
That's the integrator's mistake.
By default, Axis is set to true VBR (i.e., goes as high as it needs). So either the integrator's techs set the 'CBR' level too low or someone from the customer mucked with the settings. It's not an Axis issue.
Yes, if you sets the max bitrate too low for one's needs, either frames are going to be dropped or compression is going to be increased to compensate (see the priority option in the Axis configuration screen).