Re: CoreAudio and decoding/encoding MP3
Re: CoreAudio and decoding/encoding MP3
- Subject: Re: CoreAudio and decoding/encoding MP3
- From: William Stewart <email@hidden>
- Date: Thu, 28 Apr 2005 11:29:59 -0700
On 28/04/2005, at 7:20 AM, Ev wrote:
Peeking through CoreAudioTypes.h, I found a couple of format flags
that I'm interested in: in particular kAudioFormatMPEGLayer3 and
those handfuls of AACs.
If I wanted to use CoreAudio to decode MP3s, here are some
questions I have with such a process:
#1 - I'm assuming it's not the LAME encoder/decoder - which coder
is it, curiously?
First, we only ship a decoder, not an encoder for MP3 - and we've
been shipping this for some years now.
#2 - if I have an AUFormatter set up with MP3 as the input and
playback as the output and I ask it to render, would the
AUFormatter like it if I gave it the ID3 tag data? Will it parse
over that, or do I have to pass it raw MP3 data, jumping over the
ID3 tag stuff? (aka do I have to parse the MP3 file myself)
What's an AUFormatter?
You can't directly interface compressed data streams with Audio Units
- we've deliberately kept those two areas separate (AudioConverter
API deals with this problem space). The AudioFile API will parse
information out of an ID3 tag for Spotlight in Tiger, but we don't
have an explicit API to read/write MP3-ID3 tags.
#3 - are there any other flags in the ASBD that need note when
dealing with MP3? bytesPerPacket, bytesPerFrame, etc?
no flags for mp3. AAC you must specify the flag for the MPEG-4 Audio
Object Type.
Bill
Thanks in advance for any help!
Ev
Technical Knowledge Officer
Head Programmer/Designer
Audiofile Engineering
http://www.audiofile-engineering.com/
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