15-01-2013, 03:32 PM
Video Compression Basics
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Video compression fundaments
since a video stream has 2 spatial and 1 temporal
dimensions, video compression is usually done
independently in the spatial dimensions and,
respectively, in the time dimension
in the spatial dimensions – compression tries to
eliminate spatial redundancy (like in JPEG)
in the time dimension – compression tries to eliminate
temporal redundancy (i.e. motion of objects)
Video compression standards
there are 2 family of standards: ISO/IEC MPEG and ITUT
International Standardization Organization(ISO),
International Electrotechnical Commission (IEC) , MPEG
(Moving Pictures Experts Group) produced the MPEG
standards:
MPEG-1, 1992 : video standards for CDROMs and Internet video
MPEG-2, 1994 : video standards for television and
telecommunications standards
MPEG-4, 1999 : advanced video coding standards
MPEG-7, 2001 : metadata for audio-video streams, Multimedia
Content Description Interface
MPEG-21, 2002 : distribution, exchange, user access of
multimedia data and intellectual property management
Frame Intracoding
a frame is intracoded similar to the way a JPEG
encoder encodes images
Spatial Operator T refers to DCT (Discrete Cosine
Transform)
Quantizer Q refers to the quantization matrix
VLC refers to Variable Length Coding, i.e. run-length
encoding (including zig-zag order) plus entropy
encoding (Huffman encoding)
MPEG-1
developed by the Working Group 11 (WG11) of
SubCommittee 29 (SC29) of the Joint ISO/IEC Technical
Committee 1 (JTC 1) on Information Technology;
informally MPEG (Motion Picture Experts Group)
was developed between 1988-1990
in 1992-1994 reached an International Standard
was based on JPEG work and the ITU-T
Recommendation H.261
the goal was a coding standard for digital video and
audio motion picture for digital storage media at about
1.5 Mbps; so that the video (approx. 1 hour long) can be
stored on a CD, VCD (Video Compact Disk) – which is
approx. 648 MBytes large