CBR vs VBR

[Dirk_D 0]

I'm sure this is a very basic question but why choose one over the other?

[ak357 0]

I'm sure this is a very basic question but why choose one over the other?

http://lmgtfy.com/?q=CBR+vs+VBR

[mkkoskin 0]

Basicly CBR (Constant Bitrate) will guarantee you better quality at all times, but at a higher bandwidth cost. All the systems we install, we install with CBR.

 

Example to explain it:

You have a camera watching a door. Someone enters and rushes thru the door quickly, you would like to see who it was and get a detailed image of his/her face.

 

Case VBR (Variable bitrate): While there is no motion, bitrate is very low, and when someone enters thru door, camera raises the bitrate to handle all motion. This might cause blurriness/pixelation in the beginning of the motion, if the motion is short enough (rushing thru door, enters and leaves camera view within second for example) image might be very blurry/pixelated and person not recognizable.

 

Case CBR: Even when there is no motion, bitrate stays the same, when someone enters thru door, bitrate is enough to handle the motion and even if the person is visible only for a second, image is as clear as it is without motion.

 

So if you have a very limited bandwidth, you can try to go with VBR, but there is always a chance its wont capture everything as sharp as CBR would.

[No5 0]

Basicly CBR (Constant Bitrate) will guarantee you better quality at all times, but at a higher bandwidth cost. All the systems we install, we install with CBR.

 

Example to explain it:

You have a camera watching a door. Someone enters and rushes thru the door quickly, you would like to see who it was and get a detailed image of his/her face.

 

Case VBR (Variable bitrate): While there is no motion, bitrate is very low, and when someone enters thru door, camera raises the bitrate to handle all motion. This might cause blurriness/pixelation in the beginning of the motion, if the motion is short enough (rushing thru door, enters and leaves camera view within second for example) image might be very blurry/pixelated and person not recognizable.

 

Case CBR: Even when there is no motion, bitrate stays the same, when someone enters thru door, bitrate is enough to handle the motion and even if the person is visible only for a second, image is as clear as it is without motion.

 

So if you have a very limited bandwidth, you can try to go with VBR, but there is always a chance its wont capture everything as sharp as CBR would.

 

On my ACTi 3MP domes I set:

 

Encoder Type: H.264

H.264 Profile: High Profile

Resolution: N2048X1536

Frame Rate: 15

Video Bit Rate Mode: Constant Bit Rate

Video Max Bit Rate: Unlimited

Video Bit Rate: 6M

 

Question: Is the video bit rate setting @ 6M overkill in your opinion? Should I lower it to 4M?

[vimes 0]

Basicly CBR (Constant Bitrate) will guarantee you better quality at all times, but at a higher bandwidth cost. All the systems we install, we install with CBR.

 

Example to explain it:

You have a camera watching a door. Someone enters and rushes thru the door quickly, you would like to see who it was and get a detailed image of his/her face.

 

Case VBR (Variable bitrate): While there is no motion, bitrate is very low, and when someone enters thru door, camera raises the bitrate to handle all motion. This might cause blurriness/pixelation in the beginning of the motion, if the motion is short enough (rushing thru door, enters and leaves camera view within second for example) image might be very blurry/pixelated and person not recognizable.

 

Case CBR: Even when there is no motion, bitrate stays the same, when someone enters thru door, bitrate is enough to handle the motion and even if the person is visible only for a second, image is as clear as it is without motion.

 

So if you have a very limited bandwidth, you can try to go with VBR, but there is always a chance its wont capture everything as sharp as CBR would.

 

On my ACTi 3MP domes I set:

 

Encoder Type: H.264

H.264 Profile: High Profile

Resolution: N2048X1536

Frame Rate: 15

Video Bit Rate Mode: Constant Bit Rate

Video Max Bit Rate: Unlimited

Video Bit Rate: 6M

 

Question: Is the video bit rate setting @ 6M overkill in your opinion? Should I lower it to 4M?

 

Two of my six cameras have the same resolution as you and frame rate, I use 4M for their CBR.

I use the above resolution as the aspect ratio suits the intended area of coverage better than 1080p. Also the covered area is fairly constant in what it records, except if there were intruders or family members etc present. Thus a high bit rate, to capture lots of scene changes, is not necessary.

My other four cameras are set to 1080p and use CBR of 4M with the same frame rate. The reduced resolution has the same bit rate due to more movement and traffic etc being recorded.

[mkkoskin 0]

 

On my ACTi 3MP domes I set:

 

Encoder Type: H.264

H.264 Profile: High Profile

Resolution: N2048X1536

Frame Rate: 15

Video Bit Rate Mode: Constant Bit Rate

Video Max Bit Rate: Unlimited

Video Bit Rate: 6M

 

Question: Is the video bit rate setting @ 6M overkill in your opinion? Should I lower it to 4M?

 

I think 4Mbps should be enough for 3MP at 15fps, but really it's all about the amount of motion and lighting etc. Trial and error, you can lower it to 4Mbps and see how it handles fast motion under lowlight conditions, if there is no blur/pixelation in the stream, its sufficient.

[jhonovich 0]

"Basicly CBR (Constant Bitrate) will guarantee you better quality at all times, but at a higher bandwidth cost. All the systems we install, we install with CBR."

 

Our testing disagrees with this. Also, your description is technically incorrect.

 

CBR does not guarantee better quality. It guarantees the bit rate to be maintained. The 'quality' of CBR only comes from setting a very high bit rate to cover the worst case / most complex scenario.

 

If you set the CBR bit rate too low, you will have poor quality. If you set the CBR bir rate too high, you will waste bandwidth / storage.

 

VBR, by definition, does guarantee quality. It locks the quality / compression / quantization level, allowing the bitrate to fluctuate depending on the complexity of the scene.

 

VBR is the way to go. In our testing of dozens of leading cameras, it does not have issues maintaining quality when motion increases, because the quality level is locked, it simply increases bandwidth of the stream.

[survtech 0]

Keep in mind that different manufacturers use different interpretations for CBR. On the one hand, many define it as stated: Constant Bit Rate. Under that interpretation, the bit rate stays relatively constant under all conditions.

 

Other manufacturers use another interpretation: Constrained Bit Rate or Capped Bit Rate. With that interpretation, the setting is the maximum the device will provide but the bit rate can float down with the right conditions - low/no motion, darkness (assuming the video is "clean", with little-to-no noise), etc. This interpretation of CBR is basically the same as VBR Variable Bit Rate, but with the addition of the cap.

 

Without the cap, Variable Bit Rate devices could deliver very high bandwidths under certain conditions without actually delivering associated picture improvements. Video noise is one of the worst offenders. It can confuse an encoder into thinking the video has a high amount of motion, even when there is almost none. AGC is one of the biggest sources of video noise. In darker conditions, high amounts of AGC will cause high amounts of video noise with many devices, which can increase bit rates, often enormously.

 

Capping the bit rate while allowing it to go lower than the setting when conditions don't require it can optimize disk space. It does make storage calculations a little "iffy", though. I typically use worst-case needs when calculating storage (all bit rates at the cap) and treat the inevitable lower real average bit rate in production as a retention time benefit (ie. requirement for 30 days but in actual use, retention is maybe 35-40 days).

[mkkoskin 0]

"Basicly CBR (Constant Bitrate) will guarantee you better quality at all times, but at a higher bandwidth cost. All the systems we install, we install with CBR."

 

Our testing disagrees with this. Also, your description is technically incorrect.

 

CBR does not guarantee better quality. It guarantees the bit rate to be maintained. The 'quality' of CBR only comes from setting a very high bit rate to cover the worst case / most complex scenario.

 

If you set the CBR bit rate too low, you will have poor quality. If you set the CBR bir rate too high, you will waste bandwidth / storage.

 

VBR, by definition, does guarantee quality. It locks the quality / compression / quantization level, allowing the bitrate to fluctuate depending on the complexity of the scene.

 

VBR is the way to go. In our testing of dozens of leading cameras, it does not have issues maintaining quality when motion increases, because the quality level is locked, it simply increases bandwidth of the stream.

 

Thanks for the corrections. Obviously bit rate has nothing to do with the level of quality, but maintaining it, i though i made it clear with my explanation. But unlike your tests, we've had different results.

 

On busy malls VBR does not seem to always keep up and since there is no reason to limit bandwidth, CBR worked better. So in these cases VBR did not guarantee quality, not well enough.

 

But there are 2 settings because one works on some cases better then the other, trial and error, testing which one suits better is the way to go.

[SunnyKim 2]

Thanks for the corrections. Obviously bit rate has nothing to do with the level of quality, but maintaining it, i though i made it clear with my explanation. But unlike your tests, we've had different results.

 

On busy malls VBR does not seem to always keep up and since there is no reason to limit bandwidth, CBR worked better. So in these cases VBR did not guarantee quality, not well enough.

 

The quoted one may add some confusions among us. I agree mostly to jhonovich's explanation. To my understanding, in order to give rather constant video quality, VBR is to be used with a fixed quantization parameter. Instead, CBR changes the parameter to squeeze into a given bit stream size during a few seconds, therefore, recorded video quality can be fluctuating(good or bad quality) as a result. A good CBR algorithm can reduce these side artifacts, of course, depending on cameras and DVRs. So the decision is up to you, after testing in the field, to your satisfaction.

[jhonovich 0]

If you have quality problems with VBR, then you should look at what quality / compression / quantization level the camera is set to and adjust it.

 

VBR does not guarantee 'good video'. It guarantees that whatever quality / compression / quantization level is selected is maintained. If you or the manufacturer defaults to low 'quality' then that is what you will get.

 

Manufacturers vary on what they call this setting. Check yours. If it is called quality, increase it. If it is called compression, decrease it.

 

Here is a summary of different manufacturer names and options:

[MaxIcon 0]

I've found that VBR results depend on how the vendor implements it. On my Hiks, the VBR setting caps the maximum bit rate, so with the same bit rate setting, quality can be the same with either CBR or VBR, while bandwidth and storage usage will be lower with VBR in scenes with little motion or complexity.

 

On my older Vivoteks, VBR allows the bit rate to exceed the base setting, so VBR can, in theory, allow better quality in scenes with high complexity or motion, while consuming more bandwidth and storage space. I haven't done image comparisons on this situation to see how much difference this makes, though.