Annex 3 to AVC-598R

ISO/IEC JTC1/SC29/WG11
MPEG93/966
November 1993

Temporary Document No.7 rev2 (Daejeon)
October 29, 1993

Source:	ITU-T SG15 Experts Group for Video Coding and Systems in ATM and Other Network Environments
Title:	Spatial scalability when the base layer includes picture skipping
Relevant sub-groups: Video, Systems
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This document describes an example of workable solution for the scalability when picture skipping is involved in the base layer.

The spatial scalable encoding is modeled as follows;

1)	An input picture is downsampled to obtain the corresponding base layer picture without delay.
2)	After a complete picture is input at time "ti" to the encoder, the base layer picture is instantaneously encoded, packetized into a PES packet with stream_id "base layer video" and stored in the transmission buffer.  DTS (or PTS if the two are identical) is set to "ti+L" where L is a constant delay between the encoder input and the decoder output picture.
3)	The locally decoded base layer picture is instantaneously upsampled to the upper layer picture sampling density.
4)	The upper layer picture is instantaneously encoded by using the upsampled locally decoded picture as part of prediction, packetized into a PES packet with stream_id "upper layer video" and stored in the transmission buffer.  DTS (or PTS if the two are identical) is set to "ti+L".

The encoder (Video and Systems) must ensure that the coded data of the base layer picture, which is necessary for decoding the upper layer pictures, be made available prior to the time the upper layer pictures are decoded.  It is noted that if picture skipping is necessary in the base layer the most recently locally decoded base layer picture is used for prediction also for the subsequent upper layer pictures (e.g. Pictures 2 and 3 in the above illustration) 

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