doc.: ieee 802.11-09/0709r2 submission july 2009 carlos cordeiro, intelslide 1 lightly compressed...
TRANSCRIPT
July 2009
Carlos Cordeiro, Intel
Slide 1
doc.: IEEE 802.11-09/0709r2
Submission
Lightly Compressed Video Traffic Modeling
Date: 2009-07-02
Authors:
Name Affiliations Address Phone Email
Carlos Cordeiro Intel Corp. OR, USA 503-712-9356
V. Srinivasa Somayazulu Intel Corp. OR, USA [email protected]
Guoqing Li Intel Corp. OR, USA [email protected]
July 2009
Carlos Cordeiro, Intel
Slide 2
doc.: IEEE 802.11-09/0709r2
Submission
Objective
• As part of the TGad evaluation methodology described in 802.11/09-296r6, TGad needs to define a model for lightly compressed video
• In this presentation we propose a lightly compressed video traffic model that can be used for TGad proposal evaluation
July 2009
Carlos Cordeiro, Intel
Slide 3
doc.: IEEE 802.11-09/0709r2
Submission
Introduction
• Traffic modeling is an old discipline, but which remains very challenging
• For the specific case of compressed video traffic, a model has a high dependence on the video source and compression method used
• Here we derive a model based on a publicly available video source and compression standard, and propose that this model be used by TGad– An alternative model would be to use a random distribution, but even in
this case some level of parameter estimation is needed
– We believe such model to be reasonable for the purpose of TGad proposal evaluation
July 2009
Carlos Cordeiro, Intel
Slide 4
doc.: IEEE 802.11-09/0709r2
Submission
Video compression in 60GHz (1)
• The choice of compression technology to meet 60GHz requirements is still being debated
• However, H.264 is a popular block based compression scheme– Trace data encoded with H.264 is publicly available– Codec algorithm is widely known and reproducible
• Specific restriction on H.264 codec profiles: only intra-frame coding, no P and B frames– B frames introduce unacceptable latency > 1 frame– P and B frames introduce large memory requirements at decoder – this may
be contentious– P and B frames also introduce large error sensitivity: Intra-frame coding is
more robust to transmission errors• Therefore, for H.264-compressed video at 60GHz, we believe it is
more realistic to assume a model whereby only I frames are included
Propose to build a model for compressed video using H.264 I-only encoder
July 2009
Carlos Cordeiro, Intel
Slide 5
doc.: IEEE 802.11-09/0709r2
Submission
Video compression in 60GHz (2)
• To meet the video requirements in 11-09-0296r6 for operation in 60GHz, we need to use a modeling method that meets the 2ms latency requirement and buffer constraints
• That implies that compression at 60GHz will likely be performed at the slice level
– Slice-based compression is defined in the H.264 standard itself*
– Can define small slice sizes consistent with low latency
– E.g., for 1920x1080p video, a slice size of 16*1920*3bytes ~ 92Kbytes (except for the last slice, which is smaller)
• However, all publicly available compression traces are on a video frame basis
• We need slice-based statistics
1920
1080
16
16
...
Slice 1MB1 MB2
MB = Macro-block
Slice 2
Slice 68
...
1080p Frame
* As an example, Cavium Networks (http://www.caviumnetworks.com/) provides a low-latency H.264 based solution using this feature
July 2009
Carlos Cordeiro, Intel
Slide 6
doc.: IEEE 802.11-09/0709r2
Submission
Trace-based modeling
• A H.264 standards based codec is used to generate slice-based trace data for the lightly video compression modeling
– Used the existing CAVLC Intra 4:4:4 H.264 profile • Trace data generated from the “Breeze” video clip*
– HD 4:4:4 1280x720 30fps movie– 1280x16 slice (scaled up to 1920x16 and 60 fps for 1080p60)– Intra-frame-only encoding used: all slices are I slices (no rate control)– Compression ratio of ~ 5.8 for an average bit-rate of ~515Mbps for 1080p60 source
Compressed slice statistics
No. of slices 20745
Min/Max/Ave slice size (Kbytes) 6.7 / 21.22 / 15.8
Variance (Kbytes) 1.823
* P. Topiwala, C. Tu, “Introduction to the Viper Dataset,” ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 Q.6, Doc. #JVT-J039, December 2003
July 2009
Carlos Cordeiro, Intel
Slide 7
doc.: IEEE 802.11-09/0709r2
Submission
Proposed compressed video model (1)
• We plot the PDF of the actual slice size distribution, and the corresponding Normal distribution obtained using the Method of Moments
• The Normal distribution seems to provide a reasonable approximation to the measured video data– µ = 15.798 Kbytes
– σ = 1.350 Kbytes
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 5 10 15 20 25
Slice size (Kbytes)
PD
F
Slice data Normal(15.798,1.350)
July 2009
Carlos Cordeiro, Intel
Slide 8
doc.: IEEE 802.11-09/0709r2
Submission
Proposed compressed video model (2)
• The model is based upon one particular video sequence, compressed at one particular bit rate – Therefore, the Normal distribution on the previous slide generates mean bit rates of ~515 Mbps, and a peak
bit rate of 693Mbps
• How to generate slice sizes for different target bit rates ranging up to 3Gbps, while keeping the model simple and avoiding multiple models for different rates?
• Proposal: Scale the mean of the original Normal distribution according to the desired bit rate– But place an upper bound of 92.160 Kbytes on the slice size: size cannot exceed the raw data!
• For example:
Desired avg. bit rate Normal distribution for model
0.4*515 Mbps Normal(0.4*µ, 0.4*σ)
2*515 Mbps Normal(2*µ, 2*σ)
k*515 Mbps Normal(k*µ, k*σ)
… …
July 2009
Carlos Cordeiro, Intel
Slide 9
doc.: IEEE 802.11-09/0709r2
Submission
Proposed compressed video model (3)
• Parameters– Slice inter-arrival time (IAT) is constant and equal to 1/4080 seconds
• Since the number of slices per second = (60 fps) * (68 slices per frame) = 4080
– Slice sizes generated with a Normal distribution with µ = 15.798 Kbytes and σ = 1.350 Kbytes• Yields avg. bit rate (b) = 515 Mbps, peak = 693 Mbps
• Algorithm– Select target avg. bit rate B, such that B <= 2986 Mbps
– At each IAT, generate a slice size with the following distribution: Normal(µ*(B/b), σ*(B/b))• If slice size > 92.160 Kbytes, set slice size = 92.160 Kbytes
July 2009
Carlos Cordeiro, Intel
Slide 10
doc.: IEEE 802.11-09/0709r2
Submission
Conclusions
• To meet the stringent latency requirements, compressed video transmission in 60GHz will be done on a slice basis
• A slice-based model has been developed based on publicly available video source and a standards based H.264 codec
• The model uses a Normal distribution, with parameters that can be scaled to match different bit rates– In practice the proposed Normal distribution may or may not be
applicable to other video sources and/or bit rates, but we believe this to be sufficient for TGad purposes
• Therefore, we propose that the proposed slice-based model be used in the TGad lightly compressed video evaluation methodology
• Next steps: define target average bit rates for the simulation scenarios in the evaluation methodology