CBR vs VBR vs MBR - Surveillance Streaming

Author: John Honovich, Published on Mar 11, 2015

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

And it is not simply CODEC choice (like H.264, H.265, MPEG-4, etc.)

However, regardless of the CODEC, one still needs to choose how the video stream handles changes in scene complexity. This is where streaming modes such as CBR, VBR and MBR come into play. They have a major impact on quality and bandwidth consumption. In this report, we provide test results, a tutorial and recommendation on how to optimially choose and use streaming modes.

CBR vs VBR vs MBR

Choosing between modes is typically overlooked:

  • CBR stands for constant bit rate and, like the term implies, aims for a constant or unvarying bandwidth level
  • VBR stands for variable bit rate and, like that term implies, allows the bit rate to vary
  • MBR stands for maximum bit rate allowing the bit rate to vary but only up to a maximum value.

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

Why the Difference

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?

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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 money on storage.

IP Camera Implementation Issues

Making the choice more challenging, two common issues arise:

  • 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.
  • 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 cameras such as Arecont, Avigilon, Axis, Bosch, Dahua, Hikvision, Panasonic, Samsung and Sony.

Recommendation - Use MBR

While VBR and CBR are the most well known types, for surveillance purposes, we recommend you use MBR (sometimes called VBR with a cap). This combines 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

MBR is offered by most manufacturers in newer firmwares, though with different terminology and settings.

Cameras that support MBR provide significant benefits and should be a positive factor in camera selection. MBR can and should be used in pretty much every scene. Compared to MBR, CBR simply wastes bits. And if you really want 'pure' VBR, just set the cap really high.

Video Screencast

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:


Manufacturer Configuration Options

In this final section, we walk through the encoding configuration options for each camera.

Arecont Vision

Traditionally, Arecont Vision only had VBR, no CBR nor MBR. Now, newer firmware version support all 3 so if you have existing Arecont cameras that do not show these options, upgrade the firmware.

Here is what Arecont's current configuration options for streaming show:

The above rate limit for VBR provides the max / cap.

Avigilon

Next are Avigilon H.264 series cameras. These cameras support VBR and the recommended MBR mode. They accomplish this through using a control called "Max Bitrate". See below:

With Avigilon, bandwidth consumed will vary up to the maximum bit rate configured with the max bitrate acting as a cap.

Axis

Axis has never supported 'true' CBR. Historically, their 'constant bit rate' setting was actually an MBR but mislabelled. Recently, Axis has rectified this.

With Axis' newest 2015 firmware, here are the options for streaming:

The maximum bit rate option allows the bit rate to vary up to the number entered.

Here is what the older Axis streaming configuration options looked like.

Bosch

Bosch has the most complex configuration options for encoding of any camera we have reviewed. It can do all 3 of the modes we discussed. However, it requires understanding how to set the 'target bit rate' and 'maximum bit rate' fields shown below:

If you want CBR, set the target bit rate and the maximum bit rate close together. Bosch allows for these two numbers to be as close as a 10% difference (e.g., 5000 and 5500 for target and max respectively).

If you want VBR, make sure to set the target bit rate low and the maximum bit rate high, keeping in mind that Bosch uses the target bit rate as the minimum bit rate effectively. Also, Bosch typically sets agressively high target bit rates (to be conservative) so you likely want to lower regardless.

Finally, for MBR, with Bosch set the target bit rate as your minimum and whatever you are comfortable with as the cap in the maximum bit rate.

Dahua

Dahua IP cameras supports all 3 modes, as shown below:

The bit rate at the bottom of the red box above acts as the cap / max.

Hikvision

Hikvision IP cameras supports all 3 modes, as shown below:

The Max. Bitrate above acts as the cap / max.

Panasonic

Panasonic IP cameras support all 3 modes, but with some hybrid options. Along with CBR and VBR/Advance VBR (MBR, but with the ability to set individual image quality when the stream is viewed on multiple clients), the modes "Frame Rate" is VBR without a cap so frames are not dropped, and "Best Effort" is essentially VBR with a min/max.

The 5 modes can be seen in the example below:

Pelco

Pelco supports all 3 modes, but use what they call CVBR or 'Constrained Variable Bit Rate' encoding. Essentially, this is a CBR codec that allows the bit rate to vary modestly - say plus or minus 10%. As such, it is more or less a CBR mode. The specific bit rate or target is set in the Bit Rate field, shown below:

Samsung

Samsung IP cameras supports all 3 modes, as shown below:

The maximum bit rate shown above acts as the cap / max.

Sony

Sony now supports all 3 modes, though Sony only started supporting this in 2013/2014 so existing Sony cameras that have not had their firmware upgraded may not support VBR or MBR.

To enable MBR on Sony, select VBR and then fill in the maximum bit rate limit appropriately as shown below:

Below shows all 3 options for Sony:

Note: Sony has an option for 'adaptive rate control' but this is not true VBR. Adaptive rate control only reduces the bitrate of the stream if there is network congestion but does not vary the bit rate based on the scene complexity (as is typical with VBR). As such, adaptive rate control may be useful for congested or bandwidth limited networks like wireless or DSL connections but does not offer the benefits of VBR in normal operating conditions.

Dealing with CBR Cameras

Thankfully, CBR only cameras are increasingly becoming extinct. However, if you come across a camera that does and have to use it, here are som recommendations.

Out of the box, manufacturers of CBR cameras, typically set the default bit rate fairly high relative to common usage. This means the image quality should look good. On the negative side, this also likely means you are wasting bandwidth.

With CBR, determining the right bit rate can take one of two basic approaches:

  • Keep the bit rate set high, avoid any quality problems but probably waste 30-70% of bandwidth used.
  • Test the complexity of the scene and the quality you need, by trying a few bandwidth levels at different times of the day. Then choose.

Either way, CBR forces users to compromise. Unless the scene stays the same 24/7, you will have some tradeoffs - either wasted bandwidth or degraded quality at some points of the day. This is not an easy call and why we prefer MBR since it eliminates this tricky decision.

More

Both VBR and CBR impact compression levels, which is an important and underappreciated aspect of video streaming. Regardless of resolution selected (i.e., 720p, 1080p, etc.), the amount the video is compressed varies and the more compression, the worse the video typically looks. With VBR, the compression level is fixed, and bandwidth varies to ensure each scene is compressed at that level. With CBR, the bandwidth is fixed, so the compression level has to adjust when the scene changes. For more, read our our video quality / compression tutorial.

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Comments (25)

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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.

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

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