Hi Jan,
Here's some comments based on my review of the ambisonics draft:
3. Ambisonics With Ogg Opus
> Ambisonics MAY be encapsulated in the Ogg format by encoding with the
I would suggest replacing the normative MAY by just "can"
3.1. Channel Mapping Family 2
> This channel mapping uses the same channel mapping table format used
> by channel mapping families 1 and 255.
I would suggest saying "mapping family 1" rather than "mapping families
1 and 255" since otherwise, you have families 2 referencing itself.
Also, we don't know what families 4 and up will look like.
3.2. Channel Mapping Family 3
I would suggest removing the "Output Channel Numbering" field because it
is fully equivalent to simply permuting lines of the matrix. Also, I
believe that the size of the matrix was meant to be "32*(N+M)*C bits"
rather than "32*N*C bits".
About the matrix -- and as previously discussed privately -- I think it
should probably be stored as 16-bit integers in Q15 format. If any
global scaling is ever required, then the "output gain" field can always
be used.
> Note that [RFC7845] specifies that the identification header cannot
> exceed one "page", which is 65,025 octets. This sets a practical
> maximum ambisonic order of 10, if full order is utilized and the
> number of coded streams is the same as the ambisonic order plus the
> two non-diegetic channels.
This text is unclear about whether partial order 11 is allowed. I have
no strong opinion on the subject, but think it should be clarified.
Cheers,
Jean-Marc
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