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August 25, 2009 Video Encoding and Compression Justin Cardones (401) 441-6801 Incremental Steps: Getting to more High Definition.

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Presentation on theme: "August 25, 2009 Video Encoding and Compression Justin Cardones (401) 441-6801 Incremental Steps: Getting to more High Definition."— Presentation transcript:

1 August 25, 2009 Video Encoding and Compression Justin Cardones (401) Incremental Steps: Getting to more High Definition

2 Agenda MPEG-2 Background Deployment Techniques MPEG-4 & Transcoding A Few Ways to Get More HD

3 Compression Familiar Examples Audio CDiPodDigital camera Video DVD Compressed?NoYes Compression method --MP3, AACJPEGMPEG-2

4 Video or Audio Input Audio/Video Encoding Analog-to-Digital Conversion Encoding Compressed Video or Audio

5 Video or Audio Input Audio/Video Encoding Analog-to-Digital Conversion Encoding Compressed Video or Audio Decoding Digital-to-Analog Conversion

6 Video or Audio Input Going from Analog to Digital Analog-to-Digital Conversion

7 SDI Video Serial digital interface (SDI) 270 MHz clock 8-bit or 10-bit Video data plus timing codes (SAV, EAV)

8 SDI Ancillary Data Used for: Embedded audio (PCM or compressed) Captioning Aspect ratio signaling And more… SDI Video Data

9 Audio Compression MPEG Layer II (MUSICAM) AC-3 (Dolby) Advanced Audio Codec (AAC) Sample rateBit rate

10 CATV Channels MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz 6 MHz

11 CATV Channels MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz QAM 256 QAM 38.8 Mbps 27 Mbps QAM 64

12 CATV Channels QAM 38.8 Mbps SDI Digital Video 270 Mbps

13 CATV Channels 38.8 Mbps SDI Digital Video 270 Mbps MPEG Video Compression

14 Program sources MPEG-2 Encoders Multiplexer QAM Modulator CATV network Subscribers Digital Video System

15 Transporting MPEG Transport Stream (TS) Allows multiplexing 188-byte packets

16 Transport Rate Overall rate of MPEG stream Usually constant bit rate Includes video + audio + data Video can be CBR or VBR Null packets

17 Program sources MPEG-2 Encoders Multiplexer QAM Modulator CATV network Multiplexer Combines multiple programs Adjusts control tables (PAT, PMT) Splices advertisements Rate shaping

18 Program sources MPEG-2 Encoders Multiplexer QAM Modulator Rate shaping (limited) Encryption Forward error correction Transmit on CATV channel

19 Equipment Interconnect Ethernet UDP/IP protocol 7 transport packets per Ethernet frame 100Base-T or Gigabit

20 MPEG Video Compression Remove redundancy Take advantage of human visual system

21 MPEG Video Compression Step 1 Filtering Analog to digital conversion More filtering Clean, noise-free signal Best results

22 MPEG Video Compression Step 2 Divide image into 16x16 macroblocks

23 MPEG Macroblocks 16 x 16 pixels (adapted) Each macroblock = Four 8x8 luma blocks Two 8x8 chroma blocks 4:2:0

24 Frames vs. Fields Interlaced scanning 2 fields per frame MPEG supports field or frame encoding

25 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)

26 MPEG Picture Types Three ways to encode a picture: I (Intra-coded) P (Predicted) B (Bidirectionally predicted) IBBPBB

27 I-frames Intra-coded Similar to JPEG image Relatively large (# of bits) I BBPBB

28 P-frames Predicted Changes from previous reference frame Relatively small IBB P BB

29 B-frames Bidirectionally predicted Changes from previous or next reference frame Smallest IB B BBP

30 Motion Estimation For each macroblock: Find similar 16x16 block in reference frame Subtract them Residual Send motion vector and residual

31 BBPBB I Group of Pictures Example: GOP length = 15 I/P spacing = 3 BPBBPBBBPBB I

32 Breaking the Pattern Fixed GOP = Fixed I/B/P pattern Or encoder may insert I-frames Scene changes Splice points IBBPBB

33 Shorter GOPs: Lower latency Faster recovery GOP Length (not always) Video Quality Recommended range: Longer GOPs: Better video quality (at low bit rates)

34 MPEG Transport Stream Usually constant bit rate Elementary streams can be CBR or VBR Single or multiple programs Each has clock reference (PCR)

35 47 MPEG Transport Packet 4 byte header byte payload = 188 bytes (Plus 16 error-correction bytes = 204 bytes) 1FFF10

36 MPEG Transport Header 471FFF10 471FFF Sync bytePID (13 bits)Continuity counter (4 bits) 0

37 MPEG Transport Stream PAT PMT Null packetVideo packetAudio packet

38 MPEG Tables Program Specific Information (PSI) PAT = Program Association Table PMT = Program Map Table CAT = Conditional Access Table NIT = Network Information Table

39 PSI Tables

40 DVB and ATSC Tables 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

41 Variable Bit Rate Target bit rate range (min, max) Target video quality Bit rate changes to achieve target Varies with time Varies across program mix

42 Variable Bit Rate Easy content: News channels Cartoons Difficult content: Sports action Quick scene changes

43 EncodingRate-ShapingModulation Open-loop VBR

44 Rate Shaping Goal: Fit streams in fixed-bandwidth channel 38.8 Mbps (256-QAM) 38.8 Mbps

45 Rate Shaping Partially decode MPEG stream Change quantization Reconstruct stream Favor high-priority channels

46 Closed-loop controller Encoding Modulation Closed-loop VBR Complexity estimates Bit rate assignments

47 Modulation Encoding All-CBR Architecture

48 Ad Splicing Ads are usually CBR May need rate shaping

49 Ad Splicing Network EncoderMux/Splicer Ad Server QAM CATV Network Cue tones SCTE 104 SCTE 35 SCTE 30 Ad stream

50 MPEG-2 vs. MPEG-4

51 Moving to MPEG-4 Lower bit rates Same transport stream Upgrade encoders Upgrade set tops

52 August 25, 2009 Video Encoding and Compression Presented By:Justin Cardones (401) Derived from Original Content by Marty Sauser, EGT, inc.


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