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w3c / webrtc-svc

W3C Scalable Video Coding (SVC) Extension for WebRTC
https://w3c.github.io/webrtc-svc/
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Add note about mappings of scalability modes to AV1 #40

Closed aboba closed 4 years ago

aboba commented 4 years ago

Fix for Issue https://github.com/w3c/webrtc-svc/issues/36

aboba commented 4 years ago

@DanilChapovalov I have added a note about the mappings of the scalabilityMode values to AV1's scalability_mode_idc. Are there additional mappings we need to include in the note?

aboba commented 4 years ago

@mhoro - Can you take a look?

DanilChapovalov commented 4 years ago

I was thinking about an extensive table instead of examples for non-trivial case. It might be better to include all 4 non-trivial KEY mappings (or may be even all 8, i.e. include both KEY and KEY_SHIFT even though they map similarly), something like:

However, "_KEY" and "_KEY_SHIFT" scalability modes in this specification corresponds to the av1 scalability_mode_idc according to this table: | scalabilityMode | AV1 name of scalability_mode_idc | | L2T2_KEY | SCALABILITY_L3T2_KEY | | L2T2_KEY_SHIFT | SCALABILITY_L3T2_KEY_SHIFT | | L2T3_KEY | SCALABILITY_L3T3_KEY | | L3T2_KEY | SCALABILITY_L4T5_KEY | | L3T3_KEY | SCALABILITY_L4T7_KEY |

mhoro commented 4 years ago

Given the high probability of confusion, I think an exhaustive mapping would work well. Due to the fact that the KEY and KEY_SHIFT structures map similarly perhaps there is a clear way to indicate such more concisely. For example,

| scalabilityMode | AV1 name of scalability_mode_idc | | L2T2_XXX | SCALABILITY_L3T2_XXX | | L2T3_XXX | SCALABILITY_L3T3_XXX | | L3T2_XXX | SCALABILITY_L4T5_XXX | | L3T3_XXX | SCALABILITY_L4T7_XXX | where XXX can equal KEY or KEY_SHIFT.

aboba commented 4 years ago

@mhoro I think a comprehensive table is a good idea. Let me try adding a column to the original table to see how that looks.

mhoro commented 4 years ago

Bernard, Would you remind me how to view the changes in final document form?

aboba commented 4 years ago

@mhoro I merged the PR, so you can just clear your browser cache and look here: https://w3c.github.io/webrtc-svc/#scalabilitymodes*

mhoro commented 4 years ago

Indeed. Thanks.

The table looks good to me. I also checked the new KEY and KEY_SHIFT diagrams. They look accurate and so much cleaner than the analogous AV1 diagrams.