[Mp4-tech] ideal rate control algorithm

[Gary Sullivan]

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 
+> [mailto: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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