Re: Issue converting audio files to Apple Lossless
Re: Issue converting audio files to Apple Lossless
- Subject: Re: Issue converting audio files to Apple Lossless
- From: scott brown <email@hidden>
- Date: Mon, 15 Mar 2010 08:44:42 -0400
I actually misspoke about the ConvertFile being correct. If ConvertFile writes
kAudioFileCAFType , then the file is identical when converted back to WAV. But if ConvertFile writes
kAudioFileM4AType, the file is not identical when converted back to WAV. Apple's own "afconvert" utility has the same problem. Is this a bug, or is there really something special that needs to be done when converting to Apple Lossless to make it truly "lossless?" I can't write a truly lossless file
Example file. original wav (output given by Jason Jordan's excellent "shntool" utility):
Length:
6:40.27
Channels:
2
Bits/sample:
16
Samples/sec:
44100
Block align:
4
Header size:
44 bytes
Data size:
70623504 bytes
Chunk size:
70623540 bytes
Total size (chunk size +
8): 70623548 bytes
Actual file size:
70623548
CD-quality properties: Cut on sector boundary:
yes
Sector misalignment:
0 bytes
WAVE properties:
Non-canonical header:
no
Extra RIFF chunks:
no
Possible problems:
File contains ID3v2 tag:
no
Data chunk block-aligned:
yes
Junk appended to file:
no
I then converted it to Apple Lossless using Apple's "afconvert". I then converted that file back to WAV. Here is the resulting wav:
Length:
6:40.24
Channels:
2
Bits/sample:
16
Samples/sec:
44100
Block align:
4
Header size:
44 bytes
Data size:
70615584 bytes
Chunk size:
70616759 bytes
Total size (chunk size +
8): 70616767 bytes
Actual file size:
70616768
CD-quality properties: Cut on sector boundary:
no
Sector misalignment:
1488 bytes
WAVE properties:
Non-canonical header:
no
Extra RIFF chunks:
yes (1139 bytes)
Possible problems:
File contains ID3v2 tag:
no
Data chunk block-aligned:
yes
Junk appended to file:
yes (1 byte)
On Thu, Mar 11, 2010 at 5:32 PM, scott brown
<email@hidden> wrote:
(responding to my own post)
If I change the outputformat of my code to just convert to
aiff (and keep the reading/writing loop exactly as is), the
original wav and resulting aiff have identical audio data.
This is what I would expect.
So is there some magic foo that I need to do for Apple
Lossless that I'm missing? Is it not as simple as just
setting the output format the way that I have done?
Thanks,
Scott
link to my previous post (too large to include in the body of this message)
http://lists.apple.com/archives/Coreaudio-api/2010/Mar/msg00062.html
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