G. Valenzise*, M. Tagliasacchi*, S. Tubaro*, L. Piccarreta

Picture Coding Symposium 2007November 7-9, 2007 – Lisboa, Portugal

*Dipartimento di Elettronica e Informazione,Politecnico di Milano

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Transmit multiple video streams over a shared channel◦ Broadcast television◦ Video-surveillance◦ etc…

The channel bandwidth is limited Equal bandwidth partitioning is not

optimal

band

wid

th

time

Stream 1

Stream 2

Stream 3band

wid

th

time

Stream 1

Stream 2

Stream 3

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Find an optimal way to allocate channel bandwidth among sequences

Example: two video sequences

time

time time

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Formulate the MINAVE and MINVAR problems in the -domain

Assumptions:◦ Constant bit rate (CBR) channel◦ Frame-by-frame optimization

Find a closed form solution for the MINVAR Compare the MINAVE and MINVAR criteria

◦ Check the coding efficiency loss for the average distortion

Relax the CBR assumption◦ Temporal smoothing

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Rate-distortion operational curve of each frame can be described in the ρ-domain (He and Mitra, 2002):

ρ-domain parameters can be estimated from decoded sequences

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

(He and Mitra, 2002)

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Which is equivalent to solving

When

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

MINAVE

MINVAR

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Average distortion of MINAVE

Average distortion of MINVAR

We know (by definition!) QUESTION:

◦ What is the coding efficiency loss?

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Average distortion of MINAVE

Average distortion of MINVAR

The coding efficiency loss is

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Relax the CBR assumption◦ Introduce a shared encoder buffer to perform VBR encoding

We apply the MINVAR rate allocation while at the same time achieving temporal smoothing

For each time instant:1.Compute the CBR distortion profile2.Smooth it with the low-pass filter (He, Zen and Chen, 2005)

3.Set Dsmooth as the target distortion and compute rates Ri

Relax or tighten the rate constraint according to the current buffer level

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

H.264decoder

H.264decoder

H.264decoder

...

H.264 bitstream

H.264 bitstream

H.264 bitstream

Rate controller

H.264encoder

H.264encoder

H.264encoder

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

MINAVE

MINVARsmoothed MINVAR

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

MINAVE

MINVARsmoothedMINVAR

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Summary:◦ Proposed a MINVAR bit allocation for multiplexed

video sequences◦ The MINVAR allocation leverages on the -domain

model (but works on any exponential model, i.e. at high rates)

◦ The coding efficiency loss w.r.t. MINAVE is, on average, of 0.5 dB

Future work:◦ Apply the MINVAR approach to Scalable Video

Coding solve a discrete optimization problem…

A -domain Rate Controller for Multiplexed Video SequencesPCS 2007, November 7, 2007

Questions?