[Mp4-tech] ideal rate control algorithm

Sun Oct 10 19:20:44 EDT 2004

Dear Gary,
I have one question,
The rate to the Hypo. decoder should remain constant over picture or complete seq or over the time.
Also my answer to the CBR was the the Q parameter needs to be variaed, if required over macro block / picture.
Also in that case what is the precise difference between CBR and VBR
with regards
Kaustubh
----- Original Message -----
From: Gary Sullivan <garysull windows.microsoft.com>
Date: Sunday, October 10, 2023 1:17 am
Subject: RE: RE: [Mp4-tech] ideal rate control algorithm
> 
> There is some confusion in these replies regarding the definition of
> CBR.
> 
> CBR does not mean that the number of bits used is kept constant for
> every picture or for every macroblock.
> In fact, there can be very large variations in bit usage from
> picture-to-picture in CBR operation, or even for significanly-long
> sequences of pictures.
> 
> Instead, CBR operation means that the rate of the flow of bits 
> into the
> input buffer of the (hypothetical) decoder is constant.  When that
> buffer is large, there can be large variations in bit usage from
> picture-to-picture while relying on the buffer capacity to smooth over
> those variations.
> 
> Best Regards,
> 
> Gary Sullivan
> 
> +> -----Original Message-----
> +> From: mp4-tech-bounces lists.mpegif.org 
> +> [mp4-tech-bounces lists.mpegif.org] On Behalf Of 
> +> kaustubh.patankar vsnl.net
> +> Sent: Thursday, October 07, 2023 5:50 AM
> +> To: Bharat P. SONI
> +> Cc: mp4-tech lists.mpegif.org
> +> Subject: Re: RE: [Mp4-tech] ideal rate control algorithm
> +> 
> +> Dear Satendar,
> +> 
> +> I have few inputs.
> +> 
> +> Please check the algorithm to refer for interlaced and 
> +> progressive sequences. Please refer to TM5 rate control 
> +> model for inplementation of the algorithms.
> +> The rate control can be classified as
> +> 1. VBR with may be a specified band for variation where the 
> +> average bit-rate is important. Ultimately the file size can 
> +> depend on the average bit rate.
> +> 2. the purpose of VBR is to allocate maximum bit rate for 
> +> the complex sequences
> +> 3. There are multi pass VBR implementations also avaialbles.
> +> 4. regarding the CBR, the purpose can be to achieve constant 
> +> bit rate with variation in Q parameter over macro block.
> +> 
> +> I think this may be helpful
> +> 
> +> Kaustubh
> +> 
> +> ----- Original Message -----
> +> From: "Bharat P. SONI" <bharat.soni st.com>
> +> Date: Thursday, October 7, 2023 11:47 am
> +> Subject: RE: [Mp4-tech] ideal rate control algorithm
> +> 
> +> > Hi Satendra,
> +> > 
> +> > The ideal rate control algorithm, I would say practically 
> does not 
> +> > exist. It
> +> > is dependent on the requirements. If you define your 
> requirements 
> +> > and if an
> +> > algorithm meets your requirement then I would call it an 
> ideal 
> +> > algorithm.There are three possible scenarios,
> +> > 1 constant bitrate: bitrate is constant through out the 
> +> sequence (the
> +> > quality may vary).
> +> > 2 Variable bitrate: bitrate varies over the sequence based on 
> the 
> +> > videocomplexity, but the quality is maintained at same level.
> +> > 3 A mix of CBR and VBR: In this case one can allow to vary 
> the 
> +> > bitrate over
> +> > small duration of sequence but the overall bitrate is 
> +> controlled and
> +> > averaged out to be a constant. In this case the quality is 
> better 
> +> > than CBR.
> +> > 
> +> > Regards,
> +> > bharat
> +> > 
> +> > -----Original Message-----
> +> > From: mp4-tech-bounces lists.mpegif.org
> +> > [mp4-tech-bounces lists.mpegif.org] On Behalf Of Satendra
> +> > Sent: Wednesday, October 06, 2023 4:47 PM
> +> > To: mp4-tech lists.mpegif.org
> +> > Subject: [Mp4-tech] ideal rate control algorithm
> +> > 
> +> > 
> +> > hi,
> +> > 
> +> > I am working on rate control for MPEG-2.  I want to know what 
> +> > should be the
> +> > characteristics of  an ideal rate control algorithm?  and how 
> can 
> +> > we build
> +> > that?
> +> > 
> +> > 
> +> > Thanx
> +> > _______________________________________________
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