Transcript PowerPC Software Architecture Overview

August 25, 2009
Video Encoding
and
Compression
Incremental Steps:
Getting to more High Definition
Justin Cardones
[email protected]
(401) 441-6801
Agenda

MPEG-2 Background

Deployment Techniques

MPEG-4 & Transcoding

A Few Ways to Get More HD
Compression
Familiar Examples
Audio CD
iPod
Digital
camera
Video
DVD
Compressed?
No
Yes
Yes
Yes
Compression
method
--
MP3, AAC
JPEG
MPEG-2
Audio/Video Encoding
Video or
Audio
Input
Analog-to-Digital
Conversion
1
3
4
6
8
10
8
7
10
14
14
Encoding
Compressed
Video or
Audio
Audio/Video Encoding
Video or
Audio
Input
Analog-to-Digital
Conversion
Decoding
1
3
4
6
8
10
8
7
10
14
14
1
3
4
6
8
10
8
7
10
14
14
Encoding
Digital-to-Analog
Conversion
Compressed
Video or
Audio
Going from Analog to Digital
Video or
Audio
Input
Analog-to-Digital
Conversion
1
3
4
6
8
10
8
7
10
14
14
SDI Video




Serial digital interface (SDI)
270 MHz clock
8-bit or 10-bit
Video data plus timing codes (SAV, EAV)
SDI Ancillary Data
Used for:
 Embedded audio (PCM or compressed)
 Captioning
 Aspect ratio signaling
 And more…
Video
SDI
Data
Audio Compression



MPEG Layer II (“MUSICAM”)
AC-3 (Dolby)
Advanced Audio Codec (AAC)
Sample rate
1
3
4
6
8
10
8
7
10
14
14
Bit rate
CATV Channels
108.000 MHz
114.000 MHz
120.000 MHz
126.000 MHz
132.000 MHz
138.000 MHz
144.000 MHz
150.000 MHz
156.000 MHz
162.000 MHz
170.000 MHz
6 MHz
CATV Channels
108.000 MHz
114.000 MHz
120.000 MHz
126.000 MHz
132.000 MHz
138.000 MHz
144.000 MHz
150.000 MHz
156.000 MHz
162.000 MHz
170.000 MHz
QAM  38.8 Mbps
256
QAM
QAM
QAM
64
 27 Mbps
CATV Channels
QAM  38.8 Mbps
QAM
SDI Digital
Video
270 Mbps
QAM
QAM
CATV Channels
38.8 Mbps
SDI Digital
Video
270 Mbps
MPEG Video
Compression
Digital Video System
MPEG-2
Encoders
Subscribers
Multiplexer
Program
sources
QAM
Modulator
CATV
network
Transporting MPEG



Transport Stream (TS)
Allows multiplexing
188-byte packets
Transport Rate





Overall rate of MPEG stream
Usually constant bit rate
Includes video + audio + data
Video can be CBR or VBR
Null packets
Multiplexer
MPEG-2
Encoders
•
•
•
•
Combines multiple programs
Adjusts control tables (PAT, PMT)
Splices advertisements
Rate shaping
Multiplexer
Program
sources
QAM
Modulator
CATV
network
QAM Modulator
MPEG-2
Encoders
Multiplexer
Program
sources
QAM
Modulator
•
•
•
•
Rate shaping (limited)
Encryption
Forward error correction
Transmit on CATV channel
Equipment Interconnect
Ethernet
 UDP/IP protocol
 7 transport packets per Ethernet frame
 100Base-T or Gigabit
MPEG Video Compression


Remove redundancy
Take advantage of human visual system
MPEG Video Compression
Step



1
Filtering
Analog to digital conversion
More filtering
Clean, noise-free signal  Best results
MPEG Video Compression
Step

2
Divide image into 16x16 macroblocks
MPEG Macroblocks
16 x 16 pixels
720
480
Each macroblock =
• Four 8x8 luma blocks
• Two 8x8 chroma blocks
• 4:2:0
http://mia.ece.uic.edu/~papers/WWW/MultimediaStandards/chapter7.pdf (adapted)
Frames vs. Fields
Interlaced scanning
 2 fields per frame
 MPEG supports field or frame encoding
Film Mode




Movies filmed at 24 frames/sec
Converted to 30 frames/sec for TV
1 out of 5 fields is a duplicate
Encoder can skip duplicate (save bits)
1 2 3 4
1
2
3
4
4
MPEG Picture Types
Three ways to encode a picture:
 I (Intra-coded)
 P (Predicted)
 B (Bidirectionally predicted)
I
B
B
P
B
B
I-frames



“Intra-coded”
Similar to JPEG image
Relatively large (# of bits)
I
B
B
P
B
B
P-frames



“Predicted”
Changes from previous reference frame
Relatively small
I
B
B
P
B
B
B-frames



“Bidirectionally predicted”
Changes from previous or next reference
frame
Smallest
I
B
B
P
B
B
Motion Estimation
For each macroblock:
• Find similar 16x16 block in reference frame
• Subtract them  Residual
• Send motion vector and residual
http://mia.ece.uic.edu/~papers/WWW/MultimediaStandards/chapter7.pdf
Group of Pictures
Example:
 GOP length = 15
 I/P spacing = 3
I
BB P B B P B B P B B
I
BB P B B
Breaking the Pattern
Fixed GOP = Fixed I/B/P pattern
 Or encoder may insert I-frames
 Scene changes
 Splice points
I
B
B
P
B
B
GOP Length
Shorter GOPs:
 Lower latency
 Faster recovery
(not always)
Longer GOPs:
 Better video quality (at low bit rates)
Recommended range:
12 - 18
Video
Quality
MPEG Transport Stream




Usually constant bit rate
Elementary streams can be CBR or VBR
Single or multiple programs
Each has clock reference (PCR)
MPEG Transport Packet
47
1F
FF
10
4 byte header + 184 byte payload = 188 bytes
(Plus 16 error-correction bytes = 204 bytes)
MPEG Transport Header
47
47
Sync byte
1F
1F
FF
10
FF
PID (13 bits)
0
Continuity counter
(4 bits)
MPEG Transport Stream
PAT
PMT
Null packet
Video packet
Audio packet
MPEG Tables
Program Specific Information (PSI)
 PAT = Program Association Table
 PMT = Program Map Table
 CAT = Conditional Access Table
 NIT = Network Information Table
PSI Tables
http://www.iec.org/online/tutorials/test_dv/topic01.html
DVB and ATSC Tables



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
Service Information (SI)
Program and System Information Protocol (PSIP)
Terrestrial and satellite networks
Electronic program guide
Real-time clock
Ratings
MPEG
PSI
DVB
SI
ATSC
PSIP
Variable Bit Rate



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
Target bit rate range (min, max)
Target video quality
Bit rate changes to achieve target
Varies with time
Varies across program mix
Variable Bit Rate
“Easy” content:
 News channels
 Cartoons
“Difficult” content:
 Sports action
 Quick scene changes
Open-loop VBR
Encoding
Rate-Shaping
Modulation
Rate Shaping
Goal: Fit streams in fixed-bandwidth channel
 38.8 Mbps (256-QAM)
38.8 Mbps
Rate Shaping
•
•
•
•
Partially decode MPEG stream
Change quantization
Reconstruct stream
Favor high-priority channels
Closed-loop VBR
Closed-loop
controller
Bit rate
assignments
Complexity
estimates
Modulation
Encoding
All-CBR Architecture
Modulation
Encoding
Ad Splicing


Ads are usually CBR
May need rate shaping
Ad Splicing
SCTE 35
Encoder
Network
Mux/Splicer
QAM
Ad stream
Cue tones
SCTE 104
SCTE 30
Ad
Server
CATV
Network
MPEG-2 vs. MPEG-4
http://www.balooga.com/mpeg4.php3
Moving to MPEG-4




Lower bit rates
Same transport stream
Upgrade encoders
Upgrade set tops
August 25, 2009
Video Encoding
and
Compression
Presented By:Justin Cardones
[email protected]
(401) 441-6801
Derived from Original Content by Marty
Sauser, EGT, inc.