Annex 4 to AVC-553R
ISO/IEC JTC1/SC29/WG11
MPEG93/700
JULY 1993

SOURCE	: EXPERTS GROUP FOR ATM VIDEO CODING IN ITU-TS SG 15
TITLE	: SUMMARY OF THE DISCUSSION ON AC-LEAKY PREDICTION
Relevant Sub-group: Video

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Input materials

AVC-515 (MPEG93/547)	Considerations on AC-leaky Prediction (Japan)
AVC-530 		European stance on leaky prediction (F,UK,B,I,N,G,NL)
AVC-531 (MPEG93/599)	Cell loss resilience : simulation results on concealment techniques (France)
AVC-536 (MPEG93/620)	Cleanup of AC-Leak Syntax and Specification (AT&T)
AVC-537 (MPEG93/686)	Comparison of the Cell-Loss Resilience of MPEG-2 Main Profile and AC-leaky 		prediction (AT&T)

Comparison

Items	AC-leaky prediction
d=6	Intra slice
N=12	

Coding efficiency / picture quality	
Almost comparable (Note 1)

Note 1- False contouring is slightly visible in the sky part of 525 line Flower-garden for AC-leaky pictures (demonstration associated with AVC-537).	

Cell loss resilience	
One view: With concealment techniques where error locations are known, d=6 is visually equivalent to N<12 (AVC-537).  If error locations are unknown, concealment cannot be used.

Another view: With concealment techniques(Note 2), d=6 and N=6 are comparable in demonstration, while d=6 and N=12 are comparable in SNR (AVC-532).

Note 2 - Use of other existing techniques such as Intra motion vector concealment, use of short slice may improve this performance for both d=6 and N=12.	

Channel hopping	
After 6 frames, reasonable representation of image is available.  After 12-15 frames, almost complete image (within 1 dB) is available.	
In most cases, complete image is available after 12 frames.  In theory, the worst case requires 24 frames for obtaining complete image.	

Additional hardware complexity	
One view: trivial in the total system and in the codec chip.

Another view: not trivial in the video codec chip.	

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Conclusion

There has been no unanimous view on inclusion of the AC-leaky prediction in the standard.