Profile limitations with mixed-order ambisonics are ambiguous

[jwcullen]

§4.2 Base Profile "SHALL be able to handle up to 18 channels."

§3.6.3 implies up to 14th-order ambisonics is supported.

For full-order ambisonics it is clear than anything higher than 3rd-order would have too many channels to comply with base profile restriction.

For mixed-order ambisonics this could be read as permitting using higher order ambisonics (A17 - A224) as long as substream_count + coupled_substream_count <= 18. Is this intended?

Or is it intended that mixed-order ambisonics should only come from A0-15 when using simple/base profile?

[sunghee-hwang]

When ambisonics_mode = PROJECTION, the number of output channels after applying_demixing matrix is C (output channel count), and the C number of channels are input to IAMF Renderer. So,

• It can't be more than 16 for both simple and base.

In this sense, I don't think that v1.0 spec supports more than 3rd order.

[jwcullen]

Ok thanks. I thought that was the case. I missed this line in §7.1

The output SHALL have N = output_channel_count number of channels.