JVET-AQ0136 AHG9: Composited Pictures Information SEI [S. He, T. Biatek, J. Boyce, M. M. Hannuksela (Nokia)]

JVET-AQ0136 and JVET-AQ0188 were discussed together.

Chaired by S. Deshpande during 15:20-15:50 on 12 July 2026.

This document proposes a new SEI message for signaling composited pictures information recommended for use in the formation of one or more target pictures by compositing constituent cropped decoded pictures from one or more layers. The proposed SEI message enables subpicture-like functionality in HEVC by using its layering functionality.

JVET-AQ0136-v2 added following updates:

1. Allow rescaling: a cpi_rescaling_enabled_flag is added in the syntax and semantics, and cpi_resampled_pic_width_minus1[ i ] and cpi_resampled_pic_height_minus1[ i ] are added in the layer’s loop when rescaling enabled.
2. A cpi_atlas_flag is added, to allow grouping a list of cropped decoded pictures with same partitioning in the target picture together. The syntax element cpi_copy_pos_idx[ i ] is added to indicate the index of layer that the sizes and positions of the constituent cropped decoded picture of the i-th layer is based on partitioning parameters of the cpi_copy_pos_idx[ i ]-th layer.
3. Editorial fix in the syntax.

Instead of grid based approach, this proposal uses cropped decoded picture pixels based approach.

Asked if this is similar to PRI SEI (maybe like multiple target pictures instead of one target picture as in PRI). PRI is in VSEI V4. If we want to have multiple target pictures in one PRI, it could be done via its extension.

Why is auxiliary id needed and can it conflict with what VSP already have. It is to provide info in the SEI and is optional.