CBR vs VBR recorded video quality

I am sure this topic has been discussed before, but could not find any previous posts here. Security industry white-papers and professional installers both make their cases for either CBR or VBR to record video files.

So storage space and bandwidth aside, I am interested to hear your thoughts purely from a quality perspective on recorded video. Which encoding method will give a higher quality recorded video file, CBR or VBR?

Lets say two exact 2mp cams are looking at the same scene and both are recoding at a resolution of 1080p, with a frame rate set to 30/25 fps.

One has its bitrate set to CBR at 6144 kb/s, the other has bitrate set to VBR at 6144 kb/s and quality level 6 (highest quality VBR setting on Dahua systems).

Which recoding will give the best quality video if 6144 kb/s is the highest kb/s available for both CBR and VBR on this example system.

(Usually as the default, 1080p records at 4096 kb/s, and on Dahua systems the default encoding is CBR).

Looking forward to hearing your thoughts...

Whichever method produces the highest bit rate, and therefore the largest files, will be the best quality. It is as simple as that. Given an equal bit rate limit, and assuming no bugs in the encoder, CBR (Constant Bit Rate) will always produce equal or better quality than VBR (Variable Bit Rate), because VBR allows the camera to reduce the bit rate if it thinks it can meet your quality goal with less data. This is good for saving space, but not so good if you want the best quality without any compromises.

Some Dahua cameras are capable of going way beyond their normal bit rate limits if you use the ROI (Region of Interest) feature. Basically this feature lets you draw one or more rectangles on the video frame and tell the camera to encode these regions at a specific quality. However I've noticed that this feature bypasses the bit rate limit which is otherwise fairly low on many Dahua cameras. For example I have a particular starlight camera I use as a weather cam and I want the absolute best possible video quality from it, but the highest bit rate it allows at 15 FPS is 5888 Kbps. So what I did was enable the ROI feature and draw just one region across the entire video frame and set it to max quality. As a result the camera regularly encodes above 10 Mbps at night (when there is more noise) and sometimes closer to 20 Mbps!

For another opinion, check out posts #18 and #20 in the thread below by @john-ipvm

Smart Codec.

This specific post by @john-ipvm Smart Codec.

He did explain CBR and VBR very well there!

bp2008 said:

Some Dahua cameras are capable of going way beyond their normal bit rate limits if you use the ROI (Region of Interest) feature. Basically this feature lets you draw one or more rectangles on the video frame and tell the camera to encode these regions at a specific quality. However I've noticed that this feature bypasses the bit rate limit which is otherwise fairly low on many Dahua cameras. For example I have a particular starlight camera I use as a weather cam and I want the absolute best possible video quality from it, but the highest bit rate it allows at 15 FPS is 5888 Kbps. So what I did was enable the ROI feature and draw just one region across the entire video frame and set it to max quality. As a result the camera regularly encodes above 10 Mbps at night (when there is more noise) and sometimes closer to 20 Mbps!

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does ROI of 6 make a difference if the VBR quality is set to 6 (highest) ?

1.21 jiggawatts! said:

does ROI of 6 make a difference if the VBR quality is set to 6 (highest) ?

Click to expand...

In my experience, yes. But your results may vary.

Hi all. I have IPC-HDW5231R-ZE and it is set to h264 CBR 720p/bitrate 5k. I use it for church masses streaming. Example here . I tried use VBR with quality 6(best) and max bitrate 5k and picture was much worse with low bitrate. So I returned back to CBR because it is visibly better. Just my 2 cents.

For LPR when capturing a plate in a scene that is only 15ft wide at 120ft, and you only get 4-5 frames, I prefer CBR and 30fps.

The picture of the church, is very complex, it has a lot of color differences, light changing and small motions. This is a great place to test camera compression and video quality. The video compression has the most amount of problems with this type of picture.

@SouthernYankee Agree. I expected camera increase bitrate when VBR because of complex scene. But it did not.