JVET-AF0098 [AHG9] On temporal reversal feature in source picture timing information SEI message [Hendry, J. Nam, S. Kim, J. Lim (LGE)]
It was asserted that the current methods for assigning the value of SourcePictureTime[ 0 ] in source picture timing information (SPTI) SEI message does not work. While the method of assigning it with externally provided value may work, the other method by setting the source picture timing for that first output picture to be equal to 0 does not work since it is simply wrong.
This contribution proposes two options to overcome the asserted problem:
Option 1: when type includes temporal reversal, allow possibility to explicitly signal the elemental distance between the first picture and the last picture for the temporal reversal and the following applies:
- When the elemental distance between the first picture and the last picture is provided, the SourcePictureTime[ 0 ] is set to this value.
- When the elemental distance between the first picture and the last picture is not provided, it is constrained that the value is provided externally.
- The distance information shall not be present when the SPTI SEI message does not include temporal reversal type.
Option 2: specify a constraint such that when the SPTI SEI message includes temporal reversal picture timing type (i.e., the value of temporalReversalFlag is equal to 1), the value of SourcePictureTime[ 0 ] shall be provided by external means.
It was commented that it may not be necessary to make a change, as the picture where the SEI message occurs is the starting point where instead of counting time forward it is counted backward. An application would be able to manage this (perhaps an editorial note on this).
No action was determined to be necessary.