By Max Havir

By Max Havir

Video Compression

• MPEG1• MPEG2• MPEG4• MPEG7• MPEG21• Cinepak

• Motion JPEG A• Motion JPEG B• H.261• H.263• Sorenson Video• Divx

How Does Video Compression Work?

Process of MPEG Compression

• Translate into a YUV scale

• YUV sample ratio

• Discrete cosine transformation

• Quantization

• Runlength encoding

• Interframe compression

YUV (YCrCb) Color

Color Sub-sampling

Discrete Cosine Transformation

• DCT's (discrete cosine transforms) to organize the redundancy in the spatial directions

• Looks at the current frame and attempts to detect correlation within the image.

• The DCT does not actually do any compression, but the coefficients can be used in later steps.

Quantization• The DCT coefficients are quantized into finite

values. The less number of values the lower the quality will be.

Run Length Encoding

• 8, 4, 4, 2, 2, 2, 1, 1, 1, 1, (12 zeroes), 1, (41 zeroes)

• Code values are given based on the probability of occurrence.

I-Frame, P-Frame, B-Frame

MPEG1 vs. MPEG2

Profiles in MPEG2

MPEG 2 offers profiles that allow its use in a wider range of applications

MPEG4

MPEG-4 will allow ‘universal access’ to multimedia information, by taking into account specificities of a wide variety of networks

• Video rates ( as claimed by creators)– low (<64 kbps), – intermediate (64-384kbps), and – high (384-4Mbps) bitrates.

H.261 and H.263

• Designed for low data rates(<50Kbps) and video- conferencing

Sources

• http://www.compressionworks.com

• http://members.aol.com/symbandgrl/

• http://bmrc.berkeley.edu/frame/research/mpeg/

• http://www.apl.jhu.edu/Notes/Geckle/525759/lecture10.pdf

• www.mpeg.org

• http://mpeg.telecomitalialab.com/

Sources (cont.)

• http://leonardo.telecomitalialab.com/icjfiles/mpeg-4_si/2-overview_paper/2-overview_paper.htm

• http://www-mobile.ecs.soton.ac.uk/peter/h263/h263.html