International Telecommunication Union
Perceptual Encoder Optimization
David McNally
Genista Corp.
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
CODECs ITU-T
o
o
Video codecs have reached a very high level of sophistication
We have two mathematically “orthogonal” mainstream approaches:
1. DCT with motion estimation & F/B
prediction (MPEG family) 2. Wavelet based schemes (JPEG2000) We observe ‘similar’ quality as function of target bit-rate & frame rate:
dates ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva 2
CODECs
DCT: Wavelet:
ITU-T
Coding
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
Transmission
dates
3
CODECs
o
ITU-T
The currencies for achievable quality are:
• • • Encoder usage: 1-pass vs. n-pass Target Bitrate, frame size & frame rate Network behavior (BER, PLR, Latency, Jitter)
BLER vs. Perceived Quality
dates
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
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CODECs ITU-T
Encoders have many(!) configuration parameters… ! HOW TO CHOOSE OPTIMAL SETTINGS?
dates
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CODECs
o
ITU-T
o
CODECs are designed to handle ‘expected’ content well:
• Sports; Movies; News; Nature; …
They fail for ‘unexpected’ content:
Tape noise
dates
Tape drop-out
6
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
CODECs ITU-T
Encoders are optimized for ‘mainstream’ content ! HOW TO HANDLE ‘OUTLIERS’?
dates
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The Bottom-Line ITU-T
o
The customer does not care what technology is used The customer has expectations which depend on his setting & experience:
• • • IPTV / PPV / … ! Broadcast TV Mobile / Wireless ! Internet streaming Personalized ! High tolerance
o
Does the consumer feel he is getting good value for money?!
dates ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva 8
The Bottom-Line ITU-T
o
There is an ‘industry’ which has developed around codec performance assessments (e.g. VQEG): ! ! ! ! (Subjective) Test methodologies Quality algorithms Statistical procedures Vested interests
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
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Subjective testing
wall background
17’ LCD monitor
desk
ITU-T
100 90 80 70 60 Scores 50 40 30 20 10 0
00:00:00:00 00:04:00:12 00:04:50:12 00:05:40:12 00:06:39:24 00:07:29:24
viewer
viewing location 1
viewing location 2
curtain
viewing location 3 Viewing room (*)
Mean Opinion Score
32 kbps 128 kbps 384 kbps
00:08:19:24
00:27:19:12
00:28:09:12
00:28:59:12
Time
Variance(MOS)
dates ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva 10
00:29:49:12
Methodologies
No Reference: Measure subscriber perceived quality
ITU-T
Reference
Process the content
Processed
Measure Quality
Full Reference: Measure relative degradation
Reference Process the content Alignment Processed
Measure Quality
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
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Video Quality Metrics
No Reference:
ITU-T
o o o o
Full Reference:
o Blur o Jerkiness o Blockiness o Colorfulness o Noise o ANSI metrics o PSNR
Blur Jerkiness Blockiness Colorfulness
o MOS
dates
o MOS
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NR-MOS: Predictive Power ITU-T
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Encoder Optimization ITU-T
FR 1
Parameters
2 NR
Reference
ENCODER 3
Processed
NR
1: Technical optimization 2: Service optimization 3: Content optimization
dates ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva 14
There is Really a Difference! ITU-T
Windows Media NR Blur NR Blockiness
Apple Quicktime
NR Blur
NR Blkss
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Conclusions ITU-T
o o o o o
‘Good’ Perceived quality is the key to successful media services Encoders are mature and are reaching asymptotic performance limit Video content is highly variable User expectations are highly variable Provide cost-performance optimized services Need to integrate:
• • • Knowledge of content Knowledge of user perception & expectation Knowledge of encoder implementation
ITU-T VICA Workshop 22-23 July 2005, ITU Headquarter, Geneva
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