On ItemReferenceBox version 1 in HEIF

[podborski]

In HEIF we have this text in clause 6.6.1:

The number of SingleItemTypeReferenceBoxes with the box type 'dimg' and with the same value of from_item_ID shall not be greater than 1.

SingleItemTypeReferenceBoxes is also mentioned in a bunch of derived image items.

However, in ISOBMFF the ItemReferenceBox is defined as:

aligned(8) class ItemReferenceBox extends FullBox('iref', version, 0) {
	if (version==0) {
		SingleItemTypeReferenceBox				references[];
	} else if (version==1) {
		SingleItemTypeReferenceBoxLarge	references[];
	}
}

Allowing also item references to be specified using the SingleItemTypeReferenceBoxLarge. To me this seems to be a little bit ambiguous because I don't see a clear restriction of ItemReferenceBox to be version 0 only in the HEIF spec. I see that the mif1 brand actually mentions the iref versions 0 and 1.

Table 3 — Boxes to be supported under the mif1 brand

Hierarchy of boxes	Version	Box description
...	...	...
iref	0, 1	item reference box
...	...	...