Video Compression

VideoNerd

The R-D cost function (or RDO)

where ‘b’ is the block under consideration, ‘d’ is the decision to be made, ‘C’ is the cost to minimize, ‘D’ is the distortion if the decision ‘d’ is taken, ‘R’ is the corresponding change in bitrate, while λ is an application-dependent Lagrangian weighting factor expressing how much bits we are ready to sacrifice for a given quality, λ is usually calculated as a function of the QP value.

In JM (H264 reference codec)   λ = 0.852(QP−12)/3   exponential function of QP, the values of λ are per-calculated.

 

An encoder has to choose the decision ‘d’ for the block ‘b’ which minimizes the cost function ‘C’ over the domain of all feasible decisions.

RDO is often the main performance bottleneck in encoding if apply RDO for each motion vector in Motion Estimation. Therefore it’s not uncommon to skip RDO calculations in Motion Estimation for fast presets. 

 

Note: Bear in mind each decision pertaining to a certain block can affect on next blocks. Perhaps, the decision for the current block is R-D optimal, but this optimal decision might deteriorate coding efficiency of next blocks. 

11 Responses

  1. you are actually a just right webmaster. The web site loading velocity is amazing. It seems that you’re doing any unique trick. Furthermore, The contents are masterpiece. you have done a great process on this matter!

  2. Howdy! I know this is kinda off topic however I’d figured I’d ask. Would you be interested in exchanging links or maybe guest writing a blog post or vice-versa? My blog discusses a lot of the same subjects as yours and I feel we could greatly benefit from each other. If you might be interested feel free to shoot me an e-mail. I look forward to hearing from you! Fantastic blog by the way!

Leave a Reply

Your email address will not be published. Required fields are marked *