Re: AudioConverter MP3 decode questions
Re: AudioConverter MP3 decode questions
- Subject: Re: AudioConverter MP3 decode questions
- From: "Eric M. Aldrich I" <email@hidden>
- Date: Tue, 14 Mar 2006 16:55:37 -0800
On 14/03/2006, at 4:25 PM, Vince Shumaker wrote:
Thought I'd also forward this to the list...
Thanks!
How time a given packet represents is described by the ASBD - most
formats specify a frames per packet (for linear pcm this is 1, for
compressed its generally > 1). For instance, AAC typically represents
its data as 1024 frames/packet - apple lossless as 4096, etc...
...and for MP3 its 1152? I'd like to clarify what this should be when
I create an AudioConverter using ASBD. I know that MP3 frames have a
fixed number of 1152 samples/frame. I've also seen some of the
/Developer examples using AudioFile api to get the ASBD... and the
frames/packet value comes back as 1152.
It's 1152 for MPEG 1 Layer 3 (48, 44.1 and 32 kHz) and 576 for MPEG 2
and 2.5 Layer 3 (24 kHz and below).
So I guess that I shouldn't think about "samples per frame" vs "frames
per packet" when describing MP3. It's really just a blob of time
expressed as 1152?
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Eric M. Aldrich I
Apple Core Audio Engineering
Audio Codecs
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