1 Motivation Motivation • Video Communication over Heterogeneous Networks – Diverse client devices – Various network connection bandwidths • Limitations of Scalable Video Coding Schemes – Limited layers supported – No video format changes • Video Transcoding Provides Dynamic Solutions – Channel bandwidth adaptation – Video coding format adaptation
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1 Motivation Video Communication over Heterogeneous Networks –Diverse client devices –Various network connection bandwidths Limitations of Scalable Video.
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1
MotivationMotivation
• Video Communication over Heterogeneous Networks– Diverse client devices– Various network connection
bandwidths
• Limitations of Scalable Video Coding Schemes– Limited layers supported– No video format changes
• Video Transcoding Provides Dynamic Solutions– Channel bandwidth adaptation– Video coding format adaptation
2
Challenges in Video TranscodingChallenges in Video Transcoding
• Improve Efficiency of Video Transcoding– Large data volume
– High computational complexity
• Optimize Visual Quality for a Given Bit Rate– Human vision system (HVS) based video transcoding is desirable
D ecoding(Partia lly)
V ideoM anipu la tion
EntropyEncoding
01010111 1011011... ...
Input C om pressedV ideo S tream
O utput C om pressedV ideo S tream
V ideo T ranscoder
3
Proposed SolutionsProposed Solutions
• Exploit Foveation Property of the HVS in Video Transcoding
• Develop Fast Algorithms for Video Transcoding– DCT-domain foveation filtering technique
– Fast algorithms for DCT-domain inverse motion compensation• Local bandwidth constrained DCT-domain inverse motion compensation
• Look-up-table based DCT-domain inverse motion compensation
U niform R eso lu tionC om pressed V ideo
Foveated V ideoS tream
D ecoding(P artia lly)
V ideoM anipu la tion& Foveation
V ideoR e-encod ing
01010111 1011011... ...
Foveation E m bedded V ideo T ranscoder
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FoveationFoveation
• The Human Eye Samples Visual Field Non-uniformly– The highest sampling resolution is at Fovea
– The sampling resolution decreases rapidly as away from Fovea
• Retinal Images are Inherently Non-uniform in Spatial Resolution
Eccentricity (left eye)
Eccentricity (deg)
Cel
ls p
er d
egre
e
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Foveation ModellingFoveation Modelling• Foveated Contrast Threshold [Geisler & Perry 98]
• Foveated Cut-off Frequency fc
• Spatial Frequencies Beyond
the Cut-off Frequency is
Invisible (Foveated Image)
) (),(2
20 e
eefaexpCTefCT
• f: Spatial frequency (cyc/degree)• e: Retinal eccentricity(degree)• a: Spatial frequency decay constant