CBR vs. VBR

[John Rofrano]

Given a same bitrate which is less than ideal? Yes.

CBR will use the same number of bits for every frame (hence the name “Constant” Bit Rate). If there are enough bits for the most demanding frame, then CBR/VBR makes no difference. If, however, there is not enough bits for the most demanding frame then VBR will steal some bits from frames that don’t need it and give it to the frame that needs more thus making it look better. So in a “bit constrained” environment, VBR 2 Pass will always look better than CBR.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Terry Esslinger]

Can you define a bit constrained environment? Obviously if your video is short and will fit easily on a disk you do not need to use lower bit rate so you could probably run a CBR 8,000,000 or so (SD). So length of the video is one. Are there others? For example, if you are doing a football game where there is constant massive movement but you have only 30 minutes of SD footage. Would this benefit from a VBR 2 pass over a high constant bitrate?
Thanks

[John Rofrano]

My definition of a “bit constrained environment” is simply one where you do not have the luxury of providing enough bits to accurately represent the frame. This could be due to length, it could be due to resolution (wanting HD output) which affects size, it could be due to media limitations e.g., DVD cannot sustain more that 9MB while HD is recorded at 25MB / 50MB / 100MB. Whatever is causing you to render at a lower bitrate than originally recorded.

30 min of SD football footage can easily fit on a DVD at the max bitrate allowable so CBR will do fine. 90 min of footage cannot fit so VBR may yield better results but only if there are enough scenes without motion to steal bits from. 90 minutes of non-stop action will not allow VBR to have any benefit.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Odd Magne nilsen]

If one look at this video, what will give the best result?

https://vimeo.com/2053553

odd magne nilsen

newbie

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[John Rofrano]

VBR should give better results because there are a lot of frames with little or no movement. Set the max high so that it has enough bits to represent the grass. Unfortunately, the grass is very detailed and takes a lot of bits to represent. I’m not sure why it gets so blurry when you zoom in. The image is not that different from the zoomed out image and should be represented just as well. Was the original footage soft when zoomed?

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Odd Magne nilsen]

Canon HV20, 50i, Cine Mode.

Here is the original:

https://workingkelpie.net/aussie/knive%20sony%20forum.wmv

odd magne nilsen

newbie