Annex 7 to AVC-496R

Comparison table for spatial scalability and frequency scalability

Note - This comparison table is provisional with a purpose of stimulating further work of the members.

Comparison Item	Frequency Scalability1	Spatial Scalability	
Simulcast	
Interworking Capabilities				
1. Scalability				
resolution:	+	++2	++	
bit rate:	+	++3	++	
SNR:	+	+	+	
2. Flexibility to drop all layers and code single layer:	+	+	+	
3. Ability to code in interlaced-interlaced mode:	+	+	+	
4. Ability to code in interlaced-progressive mode:	+	++	++	
5. Ability to code in progressive-progressive mode:	+	+	+	
Coding Performance				
1. Better than simulcast efficiency:	+	+		
2. Approaching single layer efficiency:	++4	+5,6		
Network Issues				
1. Can provide robustness against cell loss:	+	+	-7	
2. Ability to provide constant bitrate on all layers:	+	++	++	
Compatibility with existing standards				
1. Compatibility with H.261 or MPEG1 on lower layer possible:	-	+	+	
2. Compatibility with MPEG2 on lower layer possible:	?	++	++	
Hardware Complexity				
1. Low additional encoder cost/complexity:	++8	+9	+	
2. Low additional decoder cost/complexity (highest layer):	++10	+11	+	
3. Low additional decoder cost/complexity (lowest layer):	++12	+	+	
4. Lowest layer bit stream software decodable:	+13	-	+14	
Functionality				
1. Short encoding delay possible on all layers:	+	+15	++	
2. Short decoding delay possible on all layers:	+	+	++	
3. Panning 	+	++	++	
4. Flexibility to have complexity/quality tradeoff at encoder 
      and decoder:	++16	+17	+	
Applications				
1. Suitable for desktop video-conferencing:	+	+	+	
2. Suitable for HDTV-TV interworking:	+	+	+	
3. Possiblity to incorporate future services:	+	++	++	

1	also includes Data Partitioning
2	more flexible
3	more flexible
4	at the expense of lower picture quality at lower layer
5	seems to be dependent on sequence
6	will depend on the bit rate in the lower layer
7	similar performance can be achieved with higher complexity hardware
8	0-25% additional memory space for two layer scheme compared to single layer encoder dependent on implementation
9	25 % additional memory space needed for two layer encoding scheme
10	no additional memory space needed compared to single layer decoder
11	25 % additional memory space needed for two layer scheme
12	underlying assumtion is the DCT size which makes decoders less complex
13	DCT size, see above
14	Simulcast may provide software decodable capability if 2x2 DCT size is used
15	This may not be possible with H.261 compatibility on the lowest layer
16	Frequency Scalability schemes can be implemented using one or two loops at the encoder to achieve complexity/quality tradeoffs
17	Also Spatial Scalability schemes may be able to trade off comlexity with quality using simple fixed upsampling filters

General Comments

The meeting also noted a Sydney MPEG contribution (MPEG'93/250) presented by HHI where the coding performance of both Spatial Scalability and Frequency Scalability schemes for SNR scalability was given. Accordingly the result for both schemes were very similar. "In fact, Frequency Scalability shows some advantages for the EDTV layer and Spatial Scalability for SDTV and HDTV". Further studies are needed to verify these results.

Figure 1 shows the application dependency of either Spatial or Frequency Scalability schemes. For ease of interoperability, it is, however, desired to identify overlapping application areas which may be represented by one single application profile.

Figure 1:	Virtual Applications Areas for Frequency Scalability and Spatial Scalability Coding Schemes

END