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
Video codecs have reached a very
high level of sophistication
o
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:
Transmission
Coding
ITU-T
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
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
4
CODECs
ITU-T
Encoders have many(!) configuration
parameters…
! HOW TO CHOOSE OPTIMAL SETTINGS?
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
5
CODECs
o
ITU-T
CODECs are designed to handle
‘expected’ content well:
•
o
Sports; Movies; News; Nature; …
They fail for ‘unexpected’ content:
Tape noise
dates
Tape drop-out
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
6
CODECs
ITU-T
Encoders are optimized for ‘mainstream’
content
! HOW TO HANDLE ‘OUTLIERS’?
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
7
The Bottom-Line
ITU-T
o
The customer does not care what
technology is used
o
The customer has expectations which
depend on his setting & experience:
•
•
•
IPTV / PPV / …
! Broadcast TV
Mobile / Wireless ! Internet streaming
Personalized
! High tolerance
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):
!
!
!
!
dates
(Subjective) Test methodologies
Quality algorithms
Statistical procedures
Vested interests
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
9
Subjective testing
wall background
17’ LCD monitor
desk
ITU-T
viewer
viewing
location 2
viewing
location 1
viewing
location 3
curtain
Viewing room (*)
100
90
80
70
Mean Opinion Score
Scores
60
50
32 kbps
128 kbps
384 kbps
40
30
20
10
00:29:49:12
00:28:59:12
00:28:09:12
00:27:19:12
00:08:19:24
00:07:29:24
00:06:39:24
00:05:40:12
00:04:50:12
00:04:00:12
00:00:00:00
0
Time
Variance(MOS)
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
10
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
Processed
Alignment
Measure Quality
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
11
Video Quality Metrics
No Reference:
ITU-T
o
o
o
o
Blur
Jerkiness
Blockiness
Colorfulness
Full Reference:
o Blur
o Jerkiness
o Blockiness
o Colorfulness
o Noise
o ANSI metrics
o PSNR
o MOS
dates
o MOS
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
12
NR-MOS: Predictive Power
ITU-T
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
13
Encoder Optimization
FR
ITU-T
1
Parameters
ENCODER
Reference
NR
2
Processed
NR
3
1: Technical optimization
2: Service optimization
3: Content optimization
dates
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
14
dates
Windows Media
ITU-T
NR Blur
Apple Quicktime
There is Really a Difference!
NR Blur
NR Blockiness
NR Blkss
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
15
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:
•
•
•
dates
Knowledge of content
Knowledge of user perception & expectation
Knowledge of encoder implementation
ITU-T VICA Workshop
22-23 July 2005, ITU Headquarter, Geneva
16