Re: kExtAudioFileProperty_AudioFile property invalid on 10.4?
Re: kExtAudioFileProperty_AudioFile property invalid on 10.4?
- Subject: Re: kExtAudioFileProperty_AudioFile property invalid on 10.4?
- From: William Stewart <email@hidden>
- Date: Mon, 7 Apr 2008 14:20:23 -0700
I think you are mis understanding what the cookie is for.
When you are encoding (going from LPCM to a compressed format, say
'aac ') then you set up the encoding converter with a bunch of
parameters, vbr, bit rate, etc. Then, as you write the file you *get*
the cookie from the converter before you are finished writing the file
out.
When you are decoding (going from a compressed format, say 'aac ' to
LPCM), you get the cookie from the file and *set* it on the converter
you are using to decode.
So, the cookie contains information from an encoding session that the
decoder needs in order to decode the stream. It may not have any
specific information about encoding settings, etc, as its primary job
is to configure a decoder, not an encoder.
In that context, I don't understand why you would set magic cookie
data on a converter you are using to encode.
Bill
On Apr 7, 2008, at 1:15 PM, Stephen F. Booth wrote:
Hello all,
I've run into a 10.4 specific problem and I'm not sure where my
mistake is. I'm trying to set the magic cookie data on an
ExtAudioFile after modifying the underlying AudioConverter (bitrate,
vbr, etc). I'm doing this using the following approach:
1) Get the AudioConverter from the ExtAudioFile
(kExtAudioFileProperty_AudioConverter)
2) If it exists, set the relevant properties (bitrate, etc)
3) Notify the ExtAudioFile of the changes
(kExtAudioFileProperty_ConverterConfig)
3) Get the magic cookie data from the audio converter
(kAudioConverterCompressionMagicCookie)
4) If the format has magic cookie data, attempt to set it on the
underlying AudioFileID (kExtAudioFileProperty_AudioFile) using
kAudioFilePropertyMagicCookieData
On Leopard, this approach works. On Tiger, attempting to get the
kExtAudioFileProperty_AudioFile results in
kExtAudioFileError_InvalidProperty (-66151).
My code is loosely based on the UseAC-AF example, specifically
WriteCookie(). In my case I am using ExtAudioFile, not AudioFile,
so I'm not certain if the magic cookie data will be pulled in
automatically (the docs don't say one way or another).
So my two questions:
a) Is there a reason why kExtAudioFileProperty_AudioFile fails on
Tiger? I couldn't find anything indicating it is 10.5-only.
b) Is my code logically broken- is it even necessary to set the
cookie in this way using ExtAudioFile?
Thanks,
Stephen
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