1. Source Coding for Video Application
Video coding is the compression or decompression of digital video. The compression is usually lossy. Historically, video was stored as an analog signal on magnetic tape. After the compact disc appeared and entered the market as a digital format. It replaced the analog audio, it became possible to also begin storing the video in digital from.

2. Most Common video codecs
H.261
MPEG-1 Part 2
H.262/MPEG-2 Part 2
H.263/MPEG-4 Part 2
H.264/MPEG-4 Part 10/AVC
H.265/MPEG-H HEVC
WMV (Windows Media Video)
AVS (Standard in China, similar to H.264)
ITU Telecommunication Standardization Sector
Moving Picture Experts Group

3. Most Common video codecs
H.261
MPEG-1 Part 2
H.262/MPEG-2 Part 2
H.263/MPEG-4 Part 2
H.264/MPEG-4 Part 10/AVC
H.265/MPEG-H HEVC
WMV (Windows Media Video)
AVS (Standard in China, similar to H.264)

4. H.261
First ratified in 1988
First digital video coding standard that was truly useful in practical
All subsequent international video coding standards have been based closely on the H.261 design,
MPEG-1 Part 2
H.262/MPEG-2 Part 2
H.263
MPEG-4 Part 2
H.264/MPEG-4 Part 10

5. H.261 Structure

6. CIF and QCIF Frame Formats

7. GOB and Resynchronization
Purpose of Group of Blocks is resynchronization
GOB starts with a sync code (binary: )
Within a GOB, encoded MBs don’t even start on byte boundaries
If there’s a bit error and you lose sync, or you join in the middle, you can’t decode the next bits (you don’t know where you are in the bit stream)
Scan for the next GOB sync code, and then you can start decoding.

8. Macroblocks Macroblock is basic unit for compression
Each macroblock is 16x16 pixels
Represent as YUV 4:2:0 data
16x16 Luminance (Y) and subsampled 8x8 Cr, 8x8 Cb
Represent this as 6 Blocks of 8x8 pixels:

9. Color Representation Requires three colors
Red (R), Green (G), and Blue (B)
Nominally requires three times B&W bandwidth
Can compressed into 1.25 – 2 times B&W bandwidth by matrix:
Luminance component (Y)
Two chrominance components (I&Q or U&V)
Luminance represent the color in black and white TV
compatible

10. RGB-YIQ conversion RGB-YUV conversion 𝑌=0.299𝑅+0.587𝐺+0.114𝐵
𝑈= 𝐵−𝑌 2.03
𝑉= 𝑅−𝑌 1.14

11. Macroblock Coding Three Rules:
Don’t send it if is hasn’t changed since last frame.
Intra-frame compression
Do DCT, Quantize, Zig-zag, Run-length encoding, and Huffman coding.
Just like JPEG
Inter-frame compression
Calculate difference from previous version of same block
Can use motion estimation to indicate block being differenced can from a slightly different place in previous frame
Same DCT/quant/Huffman coding as Intra, but data is differences rather than absolute values

12. Intra-frame compression
Intra-frame coding of Microblock is very similar to JPEG
8x8 DCT (Discrete Cosine Transformation)
Quantization
Uniform quantizer (∆=8) for intra-mode DC coefficients
Uniform threshold quantizer (∆=2,4,…,62) for AC coefficients in intra-mode and all coefficients in inter-mode
Zigzag Scan
Order coefficients in zig-zag order
Run-length encode
Huffman code
The discrete cosine transform (DCT) helps separate the image into parts (or spectral sub-bands) of differing importance (with respect to the image's visual quality). The DCT is similar to the discrete Fourier transform: it transforms a signal or image from the spatial domain to the frequency domain.

13. Inter-frame compression
Basic compression process is the same as intra-frame compression, but the data is the differences from the immediately preceding frame rather that the raw samples themselves.
Frame differencing
Often the amount of information in the difference between two frames is a lot less than in the second frame itself.
Motion estimation
Motion in the scene will increase the differences
If you can figure out the motion (where each block came from in the previous frame):
Encode the motion as a motion vector (two small integers indicating motion in x and y directions)
Encode the differences from the moved block using DCT + quantization + RLE + Huffman encoding
Basic compression process is the same as intra-frame compression, but the data is the differences from the immediately preceding frame rather that the raw samples themselves.
Often the amount of information in the difference between two frames is a lot less than in the second frame itself.

14. General Description of H.261
H.261 achieves compression by removing redundancy
Temporal redundancy: reduced by motion compensation
Spatial redundancy: reduced by DCT
Statistical redundancy: reduced by entropy coding (e.g Huffman / arithmetic coding)
Perceptual irrelevancy: reduced by quantization

15. General Description of H.261
Two type of coding applied to the frames in H.261
Intra-frame coding: (I frames)
Removes spatial redundancy by JPEG-like coding
Predictive coding: (P frames)
Reduce spatial redundancy by JPEG-like coding
Reduce temporal redundancy by motion compensation
Achieve higher compression ratio than intra-frame coding
Normally, every I frame is followed by many P frames.
A new I frame would be used when there is a scene change
When there is no scene change, I frames are inserted periodically to stop any error from propagating

16. General Description of H.261
Two type of coding applied to the frames in H.261
Intra-frame coding: (I frames)
Removes spatial redundancy by JPEG-like coding
Predictive coding: (P frames)
Reduce spatial redundancy by JPEG-like coding
Reduce temporal redundancy by motion compensation
Achieve higher compression ratio than intra-frame coding

17. Intra-Block Encoding

18. Inter-Block Encoding

19. Bitstream Structure

20. H.263
Son of H.261
Standardized in 1996
Replcaing H.261 in many applications
Basic design is very similar to H.261 (DCT/Quantization based, using intra or inter framecoding)
Numerous optional improvements to improve compression, robustness, and flexibility of use

21. H.263 Improvements SQCIF: 128x96 4CIF: 704x576 QCIF: 176x144
Half-pixel precision in motion vectors (vs full-pixel precision for H.261)
New options:
Unrestricted Motion Vectos,
Syntax-based arithmetic coding (replace RLE/Huffman)
Advance preodiction (Uses 4 8x8 blocks instead of 1 16x16 which gives better detail)
Forward and Backward frame prediction similar to MPEG
Five resolutions (H.261 only have QCIF and CIF):
SQCIF: 128x96
4CIF: 704x576
QCIF: 176x144
16CIF: 1408x1152
CIF: 352x288

22. History of video coding standards H.261/263/264, MPEG-1/2/4

23. Several MPEG standards
MPEG-1: video compression at 1.5Mbit/s, CD-ROM
MPEG-2: video compression at 2-20Mbit/s, CCIR601, HDTV
MPEG-3: dissolved (combined with MPEG2)
MPEG-4: video compression at less than 28.8kbit/s, Videophone

24. Major Applications of Video Compression
Digital television broadcasting
2 – 5 Mbps
(10 – 20 Mpbs for HD)
MPEG-2
H.264/AVC
DVD video
HD-DVD
Blu-ray Disk
4 – 8 Mbps
H.264/AVC, VC-1
Internet video streaming
20 – 600 kbps
Proprietary, similar to H.263, MPEG-4, or H.264/AVC, VC-1
Videoconferencing, videotelephony
20 – 320 kbps
H.261, H.263, H.264/AVC
Video over 3G wireless
20 – 200 kbps
H.263, MPEG-4, H.264/AVC, VC-1

25. References
H.261:
 ITU-T (1988). "H.261 : Video codec for audiovisual services at p x 384 kbit/s - Recommendation H.261 (11/88)". Retrieved
JPEG compression:
H.263:
MPEG:
2&ots=Lxyhnl7BVG&sig=4G7kQp7Kj4Qmx5OuyhgBL1dAv1k&redir_esc=y#v=onepage&q=MPEG- 2&f=false

26. Q & A

27. Arrangement of Group of Pictures (GOPs) in a Video Sequence
I = Intra-frame coding
P = Predictive coding
B = Bidirectional coding

28. Coding Order of I,B,P-frame