Re: AudioChannelLayout, channel Order, kAudioChannelLayoutTag_UseChannelBitmap
Re: AudioChannelLayout, channel Order, kAudioChannelLayoutTag_UseChannelBitmap
- Subject: Re: AudioChannelLayout, channel Order, kAudioChannelLayoutTag_UseChannelBitmap
- From: Jamie Gjerde <email@hidden>
- Date: Thu, 4 Jan 2007 11:51:47 -0800 (PST)
that is the answer i could not find in the docs, that's good news.
thanks,
jamie
Brad Ford <email@hidden> wrote:
On Jan 4, 2007, at 11:35 AM, Jamie Gjerde wrote:
> i have a quicktime file with a 5.1 audio track. i get an
> AudioChannelLayout from the track that has an mChannelLayoutTag =
> kAudioChannelLayoutTag_UseChannelBitmap. mChannelBitmap is...
>
> kAudioChannelBit_Left | kAudioChannelBit_Right |
> kAudioChannelBit_Center | kAudioChannelBit_LFEScreen |
> kAudioChannelBit_LeftSurround | kAudioChannelBit_RightSurround
>
> the exact 6 channels i am looking for, however this just tells me
> what channels are there, not what order they are in. i know that
> when mChannelLayoutTag ==
>
kAudioChannelLayoutTag_UseChannelDescriptions the channel
> descriptions are in the same order as they appear in the audio buffer.
>
> how can i know the order when there is a channel bitmap?
If an AudioChannelLayout has a bitmap, then there's only one order
the present channels can be in. This is commonly known as usb order
-- the same order in which the bits are defined in the enum in
CoreAudioTypes.h. So in the bitmap you described, the first channel
is left, then right, then center, then lfe, then Ls, then Rs.
BTW - this is not specific to QuickTime files. Anytime you encounter
an audio channel layout with a bitmap, the bitmap tells you the
channels present as well as the order.
-Brad Ford
QuickTime Engineering
>
> i have alternatives for dealing with this outside of QT -
> CoreAudio, i am just asking in this specific case when there is a
> channel bitmap if there is any
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