QC Layers
Every QC Item has one Layer. The data model has four:
Wrapper
Tests the structure/integrity of the file wrapper, or of the metadata within the wrapper.
Bitstream
Tests the structure/integrity of the encoded bitstream, or of the metadata within the bitstream.
Baseband
A test applied to the decoded essence – the video frames or audio samples.
X-check ("Crosscheck")
A verification that the values agree between multiple layers. For example, if a baseband test of video frame size has been completed, and the video frame size metadata in the format and wrapper have been examined, the X-check will verify that all values match.
Letters in the EBU QC ID
The letter at the end of an EBU QC ID reflects the Item's Layer:
| Layer | Letter |
|---|---|
| Wrapper | W |
| Bitstream | F |
| Baseband | B |
| X-check | X |
F ("Format") is used for the Bitstream layer, because B was already used for Baseband. For example, 0181F is a Bitstream Item.
When you create an Item, the edit page suggests the next free number with the letter of the Layer you chose, and updates the suggestion when you change the Layer. Older IDs with a longer ending (such as X1 or X2) stay valid.
If the letter and the Layer do not match, the Item checks panel shows a finding to review: for example "EBU QC ID ends in W but Layer is Bitstream (expected F)". It never blocks saving. Usually the Layer is what needs correcting; changing the EBU QC ID of a published Item breaks references to it, so that is decided by the Group.
Retired Layers
"Programme layout" and "Not present" are not in the data model and are no longer offered. Items that still have one of them keep it until an editor chooses one of the four Layers above; the Item checks panel points this out.