Media Compression NUS SOC CS 5248 2012 Roger
- Slides: 67
Media Compression NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
You are Here Encoder Decoder Middlebox Receiver Sender Network NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Why compress? n “Bandwidth Not Enough” n “Disk Space Not Enough” n Size of Uncompressed DVD Movie = NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Why compress? n “Bandwidth Not Enough” n “Disk Space Not Enough” n Size of Uncompressed DVD Movie = (720 x 576) pixels x 3 bytes x 25 fps x 60 sec/min x 120 min = 208. 6 GB n NTSC: 29. 97 fps (30/1. 001); PAL 25 fps NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Optical Disc Formats (1) n CD: ~650 MB n Video. CD: codec MPEG-1 n 1 X max. read speed: 1. 5 Mb/s n DVD: n 4. 7 (4. 38) GB (single layer) n 8. 5 (7. 92) GB (dual layer) n Single and dual sided (up to 18 GB) n 1 X max. read speed: ~10 Mb/s n Video codec: MPEG-2 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
JPEG Compression NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Original Image (1153 KB) 1: 1
Original Image (1153 KB) 3. 5: 1
Original Image (1153 KB) 17: 1
Original Image (1153 KB) 27: 1
Original Image (1153 KB) 72: 1
Original Image (1153 KB) 192: 1
Compression Ratio Quality Size Ratio Raw TIFF 1153 KB 1: 1 Zipped TIFF 982 KB 1. 2: 1 Q=100 331 KB 3. 5: 1 Q=70 67 KB 17: 1 Q=40 43 KB 27: 1 Q=10 16 KB 72: 1 Q=1 6 KB 192: 1 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Magic of JPEG n Throw away information we cannot see n Color information n “High frequency signals” n Rearrange data for good compression n Use standard compression NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Discard color information Y V NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) U
Color Sub-sampling n The subsampling scheme is commonly expressed as a n n three part ratio (e. g. 4: 2: 2). The parts are (in their respective order): Luma (Y) horizontal sampling reference (originally, as a multiple of 3. 579 MHz in the NTSC television system). Cr (U) horizontal factor (relative to first digit). Cb (V) horizontal factor (relative to first digit), except when zero. Zero indicates that Cb horizontal factor is equal to second digit, and, in addition, both Cr and Cb are subsampled 2: 1 vertically. Zero is chosen for the bandwidth calculation formula to remain correct. To calculate required bandwidth factor relative to 4: 4: 4, one needs to sum all the factors and divide the result by 12. NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Color Sub-sampling 4: 4: 4 4: 2: 0 4: 2: 2 4: 1: 1 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
4: 2: 2 Sub-sampling Y V NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) U
Original Image (1153 KB) 4: 2: 0
Original Image (1153 KB) “ 4: 1: 0”
Discrete Cosine Transform Demo NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Quantization DC 242 65 23 5 8 8 8 -54 -10 -4 -2 8 8 8 16 13 6 3 5 8 8 16 32 2 1 -1 -2 / 8 8 16 32 64 Quantization Table NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) 30 8 = 2 0 -6 -1 0 0 0 0 0 AC
Differential Coding 30 8 2 0 25 3 1 0 27 3 1 0 6 -1 0 0 2 1 0 0 0 4 0 1 0 0 0 0 30 8 2 0 -5 3 1 0 2 3 1 0 6 -1 0 0 2 1 0 0 0 4 0 1 0 0 0 0 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Zig-zag ordering 27 3 1 0 2 1 0 0 4 0 1 0 0 0 27, 3, 2, 4, 1, 1, 0, 0, 0, 1, 0, 0 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Run-Length Encoding 27 3 1 0 2 1 0 0 4 0 1 0 0 0 27, 3, 2, 4, 1, 1, 0, 0, 0, 1, 0, 0 (27, 1) (3, 1) (2, 1), (4, 1), (1, 2), (0, 5), (1, 1), (0, 4 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Idea: Motion JPEG n Compress every frame in a video as JPEG n DVD-quality video = 208. 6 GB n Reduction ratio = 27: 1 n Final size = 7. 7 GB NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Video Compression NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Temporal Redundancy NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Motion Estimation NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Bi-directional Prediction NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Motion Vectors NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
H. 261 P-Frame I-Frame NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
MPEG-1 B-Frame NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
MPEG Frame Pattern (1) n HDV GOP example NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
MPEG Frame Pattern (2) n Example display sequence: n IBBPBBP … n Example encoding sequence: n IPBBPBB NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Compression Ratio Frame Typical Ratio I 10: 1 P 20: 1 B 50: 1 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Sequence sequence header: • width • height • frame rate • bit rate • : NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
GOP: Group of Picture gop header: • time • : NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Picture pic header: • number • type (I, P, B) • : NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Picture NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Slice NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Slice n Slices are important in the handling of errors. If the bitstream contains an error, the decoder can skip to the start of the next slice. n Having more slices in the bitstream allows better error concealment, but uses bits that could otherwise be used to improve picture quality (worse compression). NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Macroblock NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Block 1 Macroblock = NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) Y Y U Y Y V
Structure Summary NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
For I-Frame n Every macroblock is encoded independently (“I-macroblock”) NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
For P-Frame n Every macroblock is either n I-macroblock n a motion vector + error terms with respect to a previous I/P-frame (“Pmacroblock”) NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
For B-Frame n Every macroblock is either n I-macroblock n P-macroblock n a motion vector + error terms wrt a future I/P-frame n 2 motion vectors + error terms wrt a previous/future I/P-frame NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
MPEG-1/2 File Formats n (Packetized) Elementary streams, ES & PES n Program streams PS (reliable mediums, e. g. , DVD) n Transport streams TS (for lossy mediums, e. g. , on-air broadcast) Video Source MPEG-2 Elementary Encoder Packetizer MPEG encoded streams Audio Source MPEG-2 Elementary Encoder Data Source NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) PES: *. m 2 v PES: *. m 2 a Packetizer Systems Layer MUX TS: *. ts *. m 2 t *. mpg Transport Stream Packetizer Flow chart © Manish Karir
Review: MPEG structure n ES, PS, TS n Sequence n GOP n Picture n Slice n Macroblock n Block NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
MPEG Decoding (I-Frame) 101000101 Entropy Decoding Dequantize IDCT NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
MPEG Decoding (P-Frame) 101000101 Entropy Decoding Dequantize IDCT Prev Frame NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) +
MPEG Decoding (B-Frame) 101000101 Entropy Decoding Future Frame Dequantize IDCT AVG Prev Frame NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) +
There is more… n Half-pel Motion Prediction n Skipped Macroblock n etc. NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Codecs in Daily Life MPEG Standards Bit-rate Usage MPEG-1 1. 5 Mbps VCD MPEG-2 3 -45 Mbps DVD, SVCD, HDTV MPEG-4 Scalable Quick. Time, Div. X Scalable, ½ orig. MPEG-4 Scalable, ½ H. 264 AVCHD, Cable TV, You. Tube, … H. 264/AVC H. 265/HEVC NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang) Next generation
Camcorders in Daily Life n Tape-based: DV 25 (Mini. DV, DVCAM, DVCPRO) n Capacity: 1 hour ~ 13 GB n Bitrate: 25 Mb/s (user data) n Color sampling: 4: 1: 1 n Compression ratio: ~10: 1 n Disk/Flash-based: AVCHD 1. 0 & 2. 0 n H. 264: 24 Mb/s, HD, high compression NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Codec Comparison n “M-JPEG” (e. g. , DV) versus “MPEG” Compression Technique “M-JPEG” (I-frames only) “MPEG” (Temporal compression) Compression ratio Low (10: 1 to 30: 1) High (>100: 1) Editing (frame-accurate) Easy Difficult Encoding/decoding complexity Symmetric Asymmetric Processing latency Low to Medium High Multi-generation loss Medium High n No “perfect” codec -> application dependent NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
High-Definition n Standard by ATSC n 18 different sub-formats n 720 p and 1080 i are the most interesting n 1280 x 720 x 60 p, 1920 x 1080 x 60 i (30 p) n 1080 p is non-standard, but available n 1. 4 Gb/s raw bandwidth n 10 – 20 Mb/s compressed (distribution, broadcast) n 100 – 135 Mb/s compressed (pro tapes: DVCPROHD, HDCAM; for editing) NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Consumer HD n HDV: MPEG-2 n 19 (720 p) / 25 Mb/s (1080 i) n Tape format n http: //www. hdv-info. org n AVCHD: H. 264 n 5 to 25 Mb/s n Hard disk format n http: //www. avchd-info. org/ NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Optical Disc Formats (2) n Blu-ray n Capacity: 25 GB and 50 GB n 1 X speed: 36 Mb/s n Video codec: VC-1, H. 264, MPEG-2 NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Current Codec: H. 264 n “Same quality at half the rate” n Encoding complexity: ~4 X n How: n Variable block size motion compensation n Multiple reference frames n Deblocking filter, … n Also called MPEG-4 Part 10 or AVC or MPEG-4/AVC NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Current Codec: VP 8 n Google bought On 2 Technologies in 2010, which developed VP 8 n Open-source license (H. 264 needs to be licensed for use) n Similar coding efficiency and quality as H. 264 n Uses the Web. M file format NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Next Generation Codec: H. 265 n High Efficiency Video Coding (HEVC) n “Same quality at half the rate” (over H. 264/MPEG-4 AVC) n Very high encoding complexity n Supports progressive scanned frame rates and display resolutions from QVGA (320 x 240) up to 1080 p (1920 x 1080) and Ultra HDTV (7680 x 4320) NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Hands-On n Download source code, compile and play with ffmpeg n mpeg_stat n Video ‘Surfing_short. m 2 t’ from course web site (98 MB, HDV, transport stream) n n Try different MPEG-1/2 encoding parameter NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
Impact on Systems Design n n How How : : to to package data into packets? deal with packet loss? deal with bursty traffic? predict decoding time? NUS. SOC. CS 5248 -2012 Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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