CBR vs VBR vs MBR - Surveillance Streaming

By IPVM Team, Published on Nov 21, 2017

How you stream video has a major impact on quality and bandwidth.

And it is not simply CODEC choice (e.g., H.264 vs H.265).

Regardless of the CODEC, one still needs to choose how the video stream handles changes in scene complexity. There are three key streaming modes (CBR, VBR, MBR) and one related feature (smart codecs) which drastically impact camera bandwidth:

CBR vs VBR vs MBR

Choosing between modes is typically overlooked:

  • CBR stands for constant bit rate, aims for a constant or unvarying bandwidth level with video quality allowed to vary
  • VBR stands for variable bit rate and allows the bit rate to vary but maintains a constant video quality level
  • MBR stands for maximum bit rate allowing the bit rate to vary but only up to a maximum value, effectively VBR with a cap.

You need to determine whether and how much you will allow the bit rate levels to vary.

How Scene Complexity Varies

What you are streaming can vary dramatically in complexity:

  • If you have a camera zoomed in on a white wall during the day, that is a very simple scene. For a 'good' quality level, a 720p HD / 30fps stream might need 200 Kb/s for this.
  • By contrast, if you have a camera aimed at a busy intersection, this is a very complex scene. At the same exact settings as the first scene, you might need 20x the amount of bandwidth, or 4,000 Kb/s to maintain the 'good' quality level.

The more complex the scene, the more bits (i.e., bandwidth) you need to maintain the same quality level. It does not matter how 'good' or 'advanced' your codec is, this will always be the case.

What Do You Prefer?

Surveillance Challenges

The main practical surveillance challenge is that scene complexity can vary significantly even on the same camera and across just a few hours. Set the camera to use too little bandwidth and the image quality will suffer. Set the camera to use too much bandwidth and you will waste significant amounts storage.

IP Camera Implementation Issues

Making the choice more challenging are two other common factors:

  • Defaults vary: Camera manufacturers have widely varying defaults - both in terms of encoding modes enabled and bit rates used. As such, two different camera's efficiency in using bandwidth can vary dramatically even if the frame rate and resolution are the same.
  • Terminology varies: Manufacturers often do not use the terms CBR or VBR or MBR, often creating novel controls or terminology that can be confusing to understand. It is easy to make a mistake or misunderstand what their controls allow.

Inside, we provide clear recommendations and explanations on mode choice and setup for 12 manufacturers including as Arecont, Avigilon, Axis, Bosch, Dahua, Hikvision, Panasonic, Samsung, Sony and more.

Recommendation - Use MBR

IPVM recommends you use MBR (sometimes called VBR with a cap) streaming, combining the best parts of VBR and CBR encoding:

  • Compared to a typical CBR setting, MBR often reduces bandwidth consumption by 30-70%. It accomplishes this by allowing the camera to reduce bandwidth used when the scene is simple (whereas CBR always stays locked at the fixed bit rate).
  • Compared to a typical VBR setting, MBR can reduce bandwidth consumption by 20-50%. It accomplishes this by stopping VBR bandwidth consumption from exploding (typically at night) by imposing a maximum bandwidth level. No practical quality loss is likely to occur because the dark scene reduces captured image details anyway. See: Tested: Why Lowering Bandwidth at Night is Good

Additionally, MBR allows better use of smart codecs (discussed below), which CBR does not. Given the bandwidth savings of smart codecs in our tests (50%+ on average in addition to reductions mentioned above), this is an even more compelling reason to use MBR.

Smart Codecs Further Savings (Requires MBR/VBR)

In the past few years, smart codecs have become common, with most camera manufacturers including them on their cameras. Smart codecs vary compression based on what is in the scene, so static background areas may be highly compressed/lower quality while moving objects remain lower compression. Additionally, they may vary the I-frame interval, switching to a low interval and lowering bandwidth when there is little activity in the scene.

Since smart codecs vary compression, I-frame interval, and other codec settings, they require VBR or MBR by nature and are generally not used with CBR. Indeed, most cameras automatically switch streaming mode to VBR when turning smart codecs on, seen below in an example from a Dahua camera's web interface.

Note that some cameras allow CBR to be set after turning on smart codecs, but in our tests this was simply incorrect, with streams reacting the same as when VBR with smart codecs was used.

Impact Of VBR, CBR, And MBR

The video screencast below shows you VBR, CBR and (MBR) VBR Plus a Cap in action. We demonstrate the impact on bandwidth use across 4 scenes - daylight simple, daylight with motion, night time and super high motion.

If you are not familiar with the consequences of using different streaming modes, please watch this video:

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Comments (29)

John,

You might note that at least some manufacturers use the term "CBR" for Capped Bit Rate, which is essentially MBR.

Which ones?

In total, at least IV, maybe more ;)

IndigoVision might want to examine why they would (mis)use a long standing accepted industry acronym then.

You still have like to put down IV, don't you? Actually, they only offer one form of primary encoding and it is Capped Variable.

Why not pick on Axis, whose VBR is also basically capped? I believe the Bosch encoders we tested were the same.

"Why not pick on Axis, whose VBR is also basically capped?"

That's false. Their VBR is uncapped. Their MBR mode is capped. If you would have read the post you would have known that.

Maybe not by your definition but when I tested Axis encoders and P-series cameras in 2012/2013, neither exceeded the bit rate set in VBR under any conditions. That would fit my definition of capped.

With Axis, in VBR, you do not set a bitrate, period. If you were setting a bit rate, you were not in VBR mode. The old 'constant bit rate', now 'maximum bit rate' is where a specific bit rate is set.

How old? I would have to re-read my notes on the tests, but I do recall setting a bit rate and the cameras and encoders did not exceed the setting but did throttle down substantially with good light and/or no motion. Isn't that the definition of capped bit rate?

I take that back. On re-reading my notes, Axis' CBR capped the bit rate but allowed it to go substantially lower under better conditions. And you are correct: VBR bitrates were allowed to climb without apparent cap.

My bad on the VBR.

Like Carl, I was under the impression the CBR is MBR.

Can someone please give an example of a manufacturer who lists CBR as anything but constant bit rate? (outside of IndigoVision)

John,

You are sure putting a lot of effort into this Jihad against IndigoVision. You won't test their products and dismiss them, saying no one is interested, so what is the point on whether they use CBR to describe Constrained Bit Rate or Constant Bit Rate?

This reminds me of your former dislike of Avigilon. You've apparently made peace with them, why not with IV?

My issue is with you, not IndigoVision.

Ever since you bought IndigoVision, you've polluted IPVM with your whining about IndigoVision.

You want to be an IndigoVision fanboi, that's fine, just not on IPVM.

Whining? LOL.

A lot of this seems very useful to me. It may well help me deal with crowd problems encountered with the cameras in our stadium.

This was an excellent sessions. Very valuable when trying to throttle and make your video the best it can be. We spend so much time looking at video compression with Surveillance manufactures. This helps to cut to the chase.

Thank you

Frank

Geary Technologies

Northbrook, Il.

Thanks, Frank. You may also want to see our report Tested: Lowering Bandwidth at Night is Good. We specifically discuss and show examples of capped VBR video at night and the image quality and bandwidth differences (or lack therof).

John I guess article need revision - especialy term MBR looks new injected term which not commonly accepted accross IT. Before you using this, when talks about encoding technology, others as Multiple Bit Rate (MBR). Which is something different. MBR in your description is VBR with MAXRATE (terminology aka ffmpeg). I guess industry not need more confusing acronyms...

Richard, we are sticking with MBR as it emphasizes the 'maximum' element which distinguishes itself from variable bit rate.

As for multiple bit rate, I have never seen anyone use 'multiple bit rate' with the video surveillance industry.

There is no acronym or term that is going to be universally best but we think MBR is overall the strongest term to describe the use of max / cap bit rates in video surveillance systems.

John, I have to disagree

a] I have to say that "Multiple bit rate" encoding I played around in past. However never seen MBR in CCTV before read your article. So I guessed it is my ignorance but my opinion currently is that this is something what developed some cctv forum much later.

b] It will not be problem if realy accepted in industry and not in same places when comes talks about encoding. Try google "CBR VBR MBR" at once and you will see - it looks historicaly Multiple Bit encoding are much sooner here that Maximum Bit and used by quite significant players in encoding technology.

c] VBR is in fact already MBR because in real implementations VBR is every time maxrated - never could run out of limits, cause they are of course limited by input buffer, fps etc. which can be in fact recalculated to maxrate. There is nothing as "unlimited" VBR.

BTW I guess also that stat "What stream do you preffer" is misleading because respondents not aware about it. So there are not 3 categories but just two = CBR and VBR.

VBR is in fact already MBR because in real implementations VBR is every time maxrated

In the video surveillance industry, your assertion is simply not true. Historically most VBR implementations in video surveillance did not support a max rate. You can all them unreal or fake but that is reality.

Because of this, maximum bit rate is an important differentiator.

If understand you right you mean that some product in industry had "button maxrate" and others does not even they was maxrated... Well, John I understand fully meaning but in such case MBR realy starts shifting among marketing terms... on other side CBR, VBR are quite well technicaly understand.. so mixing those together in one sentence is like some marketing department doing it. Instead use "VBR with MAXRATE" is much better. And year ago I doubt there was still product without maxrate when you asked repondents. Additionaly statistics about CBR/VBR/MBR in stat are then like question "Do you know that you have there maxrate knob for VBR"? So answer is that ~44% people do not know about them (38% of 38%+48%)...

Try google "CBR VBR MBR" at once and you will see - it looks historicaly Multiple Bit encoding are much sooner here that Maximum Bit and used by quite significant players in encoding technology.

Yes, Microsoft with Multiple Bit Rate shows up first.

But I see more references from Axis camera manuals (using Maximum Bit Rate, MBR) than anything else. Do you not see these?

Microsoft is more significant, but Axis is more significant in this industry, no?

It depends if more significantly talks about encoding or about cctv marketing. I guessed originaly that this is about technical aspects of stream codec/encoding. At least you should revise definition into:

  • MBR stands for VBR where maximum bit rate is defined by user

We have experienced issues using VBR on some models of Dahua cameras. Specifically their 12MP fisheye domes. They have some flashing issue that happens when using VBR (MBR). We had to resort to CBR in order to keep the flashing from happening. 

When you use VBR with a cap or max, what is the suggested cap? Here is one of my office cameras.

 

 

 

A good explanation

Very interesting. One thing I notice is why is there streaming when the eye chart alone? 

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