Re: [Libquicktime-devel] qtinfo vs qtdump multichannel audio info

[Steven S. <sch...@gm...>]

On Fri, Mar 6, 2015 at 3:40 AM, Burkhard Plaum <
bur...@ig...> wrote:

> Hi,
>
> To my understanding (and in other audio systems), "Surround" channels
> always mean
> rear channels.


It's true that is  how many people set their systems up.  And it was the
usual layout for the quadraphonic systems in the 1970s.- ahead of its time
- the format failed then but today is back with more channels than ever.

I remember that this stuff was extremely poorly documented, it wasn't
> even a Quicktime documentation. It was a documentation of the Apple
> "Core audio format" and by accident I found out that the multichannel
> definiton is the
> same as the chan atom in Quicktime files. So it can well be that I guessed
> the
> meanings of the channels somewhat wrong.


Seems that accidents are how much of Apple's formats are discovered.  It
was by accident that I stumbled into this "problem" - I was assigning, in
the Quicktime 7 application, the channel layout of a Quicktime file's audio
track and selected the wrong choice.  Both 'surround left/right' and
'surround rear left/right' were offered.  I picked the 'rear' and then
qtinfo was saying unknown but the AV receiver played the file fine.  So off
to the mailing list and here we are :-)

>
> Can be. But I still wonder if there is a system with "Surround" plus "Rear
> Surround"
> speakers, where would they exactly be located? Are the channel positions
> better
> documented by now?


In a 5.1 system the surround speakers are almost parallel to the listening
position but slight behind.   It's in a 7.1 system that the rear surrounds
are directly in back of the listening position.

I'll include a picture from my AV Receiver's manual showing the speaker
positions for up to  an 11.1 system

But the extreme low limit of message size on the mailing list might delay
things until the message is manually approved.

> ALSO needed is a 'Mono' mapping (id #42 as I recall) which is easy enough
> > to add.
>
> Go ahead :)


will do - that's today's project


>
> > Is there nothing that could be done to clean 'em up and perhaps remove
> some
> > of the redundancy?
>
> Yes, if you are an Apple Engineer with enough influence to make an
> incompatible
> change to the Quicktime format....
>
>
I'll see what I can do :)

Cheers,
Steven