Multimedia Software Systems CS4551
Video Compression Standards
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Video Standards
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• VideoStandardsandImplementation
– Motion JPEG, Motion JPEG2000
– ITU-T Standards : H.26x (e.g. H.261, H.263, etc.)
– ISO Standards : MPEG-x (e.g. MPEG-1, MPEG-2, etc.)
• ITU (International Telecommunication Union)
– ITU-T (ITU Telecommunication Standardization Sector)
– ITU-T Video Coding Experts Group (VCEG)
• ISO (International Organization for Standardization)
– MPEG (Motion Picture Experts Group)
• JPEG is a joint working group of the International Standardization Organization (ISO) and the International Electrotechnical Commission (IEC)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Video Standards (2)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
What Do the Standards Specify?
• A video compression system consists of the following: – An encoder
– Compressed bit‐streams – A decoder
• What parts of the system do the standards specify?
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
What Do the Standards Specify? • Nottheencoder,notthedecoder.
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
What Do the Standards Specify?
• Justthebit‐streamsyntaxandthedecodingprocess,for example it tells to use IDCT, but not how to implement the IDCT.
• Enablesimprovedencodinganddecodingstrategiesto be employed in a standard‐compatible manner.
CSULA CS451 Multimedia Software Systems by Eun-Young Kang
Video Standards
APPLICATION
Motion JPEG
Continuous-tone still-image compression
Video telephony and teleconferencing over ISDN
p × 64 kb/s
Video on digital storage media (CD- ROM)
Digital Television
Video telephony over PSTN
< 33.6 kb/s
Object-based coding, synthetic content, interactivity
From Low bitrate coding to HD encoding, HD-DVD, Surveillance, Video conferencing.
Extension of H.264, support UHD, HDR, wide color bit depth and gamut
CSULA CS451 Multimedia Software Systems by Eun-Young Kang
• MotionJPEG
Motion JPEG
– A digital video sequence can be represented as a series of JPEG pictures. The advantages are the same as with single still JPEG pictures – flexibility both in terms of quality and compression ratio.
– The main disadvantage of Motion JPEG (a.k.a. MJPEG) is that since it uses only a series of still pictures it makes no use of video compression techniques. The result is a slightly lower compression ratio for video sequences compared to “real” video compression techniques.
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Motion JPEG-2000
• MotionJPEG-2000
– As with JPEG and Motion JPEG, JPEG 2000 can also be used to represent a video sequence. The advantages are equal to JPEG 2000, i.e., a slightly better compression ratio compared to JPEG but at the price of complexity.
– The disadvantage reassembles that of Motion JPEG. Since it is a still picture compression technique it doesn’t take any advantages of the video sequence compression. This results in a lower compression ration compared to real video compression techniques.
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Main Proposed Digital Video Standards
• ITUstandards
– H.261 (videoconferences over ISDN)
– H.263 (videoconferencing and video telephony over POTS)
• ISOstandards
– MPEG-1 Part 2(movies on CD-ROM)
– MPEG-4 Part 2(more versatile distribution)
• JointEffort
– H.262/MPEG-2 Part 2(digital television, movies on DVD)
– H.264/MPEG-4 Part 10 (AVC – Advanced Video Coding, HD-DVD)
– H.265/MPEG-H Part 2 (HEVC – High Efficiency Video Coding, UHD)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Video Compression – ITU-T Standards
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
• The first member of the H.26x family of video coding standards.
• The ITU H.261 standard was initially designed for Integrated Services Digital Network (ISDN) and was intended to support video conferencing applications, which have relatively small amounts of motion (mainly head and shoulder movements).
• It supports the following features
– Produces bit-rates of p×64 Kbps (p ranges 1 to 30)
– Requires the video encoders delay to be less than 150ms so that the video can be used for real-time bidirectional teleconferencing
– Only non-interlaced video
– Use YCbCr color model and performs 4:2:0 chroma subsampling
– Only CIF (352×288 for Y) and QCIF (176×144) formats
– Can encode in intraframe and interframe mode
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Common Intermediate Format (CIF)
• QCIF (Quarter CIF)
• SQCIF (Sub Quarter CIF)
• 4CIF (4× CIF)
• 16CIF (16× CIF)
• Format used to standardize the horizontal and vertical resolutions in pixels of YCbCr sequences in video signals, commonly used in video teleconferencing systems. It was first proposed in the H.261 standard.
• The CIF "image sizes" were specifically chosen to be multiples of macroblocks (i.e. 16×16 pixels) for compression.
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
– Interval between I-frames is a variable and is determined by the encoder. Usually a couple of I-frames per second.
– Motion vectors is measured in pixel unit and ranges -15 vector 15 CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
• Intraframe(I-frame):
– treated as independent image
– Macroblock : 16×16 for Y, 8×8 for Cb|Cr
– DCT on 8×8 blocks (like JPEG). Y macro block will be divided into 4 8×8 blocks.
– Quantization
• Use a constant (not 8×8 quantization table). 8 for DC coefficients, 2×𝑠𝑐𝑎𝑙𝑒 for AC coefficients where 𝑠𝑐𝑎𝑙𝑒 is a value in the range of [1,31].
• QDCT = round (DCT/8) for DC
• QDCT = floor(DCT/(2*scale)) for AC
– Zigzag code and entropy coding (arithmetic coding)
– Usually H.261 generates a couple of I-frames per second. CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
• Interframe(P-frame):
– Not independent. Coded by a forward predictive method which current
macroblocks are predicted from the previous I-frame or P-frame
– Prediction - Find the best matching block and computes motion vectors on 16×16 macroblocks from the previous frame. This previous frame is called the reference frame and it is encoded as I-frame or P-frame.
– Encode the difference macroblock (residual image)
– Encode the difference motion vectors. (MVD = MVpreceding – MVcurrent)
– If the best matching can not be found (i.e. the error exceeds a certain acceptance level), the macroblock itself is then encoded.
– Quantization (same as the I-frame)
– Zigzag code and entropy coding
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
• Improved video coding standard for video conferencing and other audio-visual services transmitted on POTS (Plain Old Telephone System) or PSTN (Public Switched Telephone Networks)
• H.263 is part of the H.324 standard for communication over POTS with a modem with a maximum available rate of 33.6 Kb/s and a normal available bit-rate of 26-28 Kb/s
• Supports a wider range of picture formats, including 4CIF (704×576 for Y) and 16CIF (1408×1152) in addition to QCIF and CIF.
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
• Based on the same DCT, motion compensation and variable-length coding (using a Run-Level variable-length code) technique used in H.261.
• Incremental improvements are
– Coding error vector instead of the motion vector itself
• The prediction starts from taking median values of the motion vectors of “previous”, “above”, and “above-right” macroblocks.
• Motion vector for current macroblock : MV(u, v)
• Motion vector for previous macroblock : MV1(u1, v1)
• Motion vector for above macroblock : MV2(u2, v2)
• Motion vector for above-right macroblock : MV3(u3, v3)
• up = median(u1, u2, u3)
• vp = median(v1, v2, v3)
• Instead of coding MV(u,v), compute the error vector (eu, ev) = (u-up, v-vp) and encode
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
• Incremental improvements are
– Half-pixel motion compensation to reduce the prediction error
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Pixel-accuracy Motion Compensation
The Reference frame A target macro block at (4,4) at the current frame
Matching with a candidate/reference block at d=(-1,-1)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Half-pixel Motion Compensation
The Reference frame A target macro block at (4,4) at the current frame
Matching with a candidate/reference block at d=(-0.5,-1)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Pixel-accuracy Motion Compensation
The Reference frame A target macro block at (4,4) at the current frame
Matching with a candidate/reference block at d=(-1, 0)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Half-pixel Motion Compensation
The Reference frame A target macro block at (4,4) at the current frame
Matching with a candidate/reference block at d=(-0.5,-0.5)
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
Generating Half-pixel Motion Block
• Dependingonthemotion,generatepixelsusinga through d.
CSULA CS451 Multimedia Software Systems by Eun-Young Kang
• Optional coding mode of H.263
– Unrestricted motion vector mode. Range is [-31.5~31.5]
– Syntax-based arithmetic coding mode
– Advanced motion prediction mode
• Overlapped block motion estimation (In luminance image, 16×16 block is divided into four 8×8 and produce 4 motion vectors to give precise description of motions→better compression)
– B-frame mode (version 2) –frame encoded by Bi-directional motion estimation
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
H.263+ and H.263++
• FullybackwardcompatiblewithH.263
• DevelopedafterMPEG-1and2soitadoptsmany aspects of the MPEG such as SNR scalability and better bidirectional prediction.
CSULA CS4551 Multimedia Software Systems by Eun-Young Kang
H.264 & H.265
• WillbecoveredafterMPEGcompressionstandards.
CSULA CS451 Multimedia Software Systems by Eun-Young Kang
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