RE: ExtendedAudioFile (AAC issue)
RE: ExtendedAudioFile (AAC issue)
- Subject: RE: ExtendedAudioFile (AAC issue)
- From: thomas rettich <email@hidden>
- Date: Thu, 2 Aug 2007 22:51:46 +0100
- Importance: Normal
> How are you computing that you are missing 2112 frames?
I am retrieving the total frame count of the file with the ExtendedAudioFile kExtAudioFileProperty_FileLengthFrames
property.
So with AAC files if it tells me x frames total, it doesn't actually read x frames but after (x-2212) frames it keeps
returning 0 frames if I try to read any further.
Is this expected ?
(if I use iTunes to convert the same file to AAC I can actually read the whole amount of frames that kExtAudioFileProperty_FileLengthFrames tells me in the first place).
Thanks,
Thomas
----------------------------------------
> CC: email@hidden
> From: email@hidden
> To: email@hidden
> Subject: Re: ExtendedAudioFile (AAC issue)
> Date: Thu, 2 Aug 2007 11:57:20 -0700
>
>
> How are you computing that you are missing 2112 frames? number of
> packets times 1024 frames per packet? If so, you are missing the fact
> that the AAC encoder has 2112 frames of priming which do not show up
> in the output. This priming info is encoded into CAF files and can be
> obtained. Different encoders may have different priming.
>
>
> On Aug 2, 2007, at 11:44 AM, thomas rettich wrote:
>
> >
> > Hi,
> >
> > I use extendedAudio file API to write and read compressed AAC files.
> > My file writing code is based on the RecordAudioToFile (sample code).
> > ASBD = {44100.0, kAudioFormatMPEG4AAC, 0, 0, 1024, 0, 2, 0, 0};
> >
> > when I try to read the AAC files created with ExtendedAudioFileRead,
> > all works fine,
> > except,
> > I cannot read the last 2112 frames.
> > ExtendedAudioFileRead always returns 0 frames, for these remaining
> > ones.
> >
> > could there be a problem in the file writing sample code, or is
> > there something I have to set up in the reading
> > with extended audio file to be able to extract all frames ?
> >
> > Any hints on how to sole this would be much appreciated!
> >
> > Thanks in advance,
> >
> > Thomas
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