JVET-AL0096 AHG9: On signalling of extension syntax elements in NNPFA SEI message [C. Kim, H. Tan, J. Nam, J. Lee, J. Lim, S. Kim (LGE)]

Chaired by S. Deshpande on 27 March 2025 at 08:30

The current design of the NNPFA SEI message in VSEI V4 determines the presence of extended syntax elements using more_data_in_payload( ). It is asserted that using only that function may cause backward compatibility such that a VSEI V4 decoder may misinterpret byte alignment bits in a VSEI V3 bitstream as extended syntax elements.

This contribution proposes to add additional check using payload_extension_present() to distinguish between byte alignment bits and extended syntax elements, ensuring backward compatibility.

The proponent commented that this is an asserted bug-fix.

It was commented that what is proposed is needed but not sufficient. JVET-T0048 provides an example to use the extension correctly and that meeting’s minutes capture the decision to do it correctly. Thus it is proposed to add SeiExtensionBitsPresentFlag = 1 inside the two if statements.

Decision: Agreed to fix the bug as proposed with additional change which makes the bug-fix as follows:

 if( more_data_in_payload( ) )

          if( payload_extension_present( ) ) {

              SeiExtensionBitsPresentFlag = 1

… }