RE: Decoding compressed audio to LPCM
RE: Decoding compressed audio to LPCM
- Subject: RE: Decoding compressed audio to LPCM
- From: Waverly Edwards <email@hidden>
- Date: Tue, 03 Jul 2018 19:07:40 +0000
- Thread-topic: Decoding compressed audio to LPCM
You are absolutely right!
I made some errors in my code that worked under certain conditions.
I mistakenly concluded it was due to the difference between the compressed and
non-compressed formats.
Once you shook that misconception, I was able to see my error.
Thank you for clearing that up,
W.
From: Matt Ingalls [mailto:email@hidden]
Sent: Monday, July 02, 2018 5:58 PM
To: Waverly Edwards <email@hidden>
Cc: CoreAudio <email@hidden>
Subject: Re: Decoding compressed audio to LPCM
I do exactly that (in Obj-C) with AAC files and the AVAudioPCMBuffer’s
floatChannelData is indeed raw PCM data.
On Jul 2, 2018, at 1:36 PM, Waverly Edwards
<email@hidden<mailto:email@hidden>> wrote:
Would someone provide guidance on how I can decompress M4A and AAC files into
memory as raw LPCM.
I need to decompress M4A and AAC files, manipulate and recompress the files
back to disk.
Writing data from LPCM to M4A or AAC is not a problem (except AAC file
durations are always wrong but will play)
I can read .caf, .m4a, .aac files into the buffer using the below code but only
the .caf files are actually raw and allow me to work directly with the buffer
contents
let file = try? AVAudioFile(forReading: url)
let buffer = AVAudioPCMBuffer(pcmFormat: file!.processingFormat, frameCapacity:
AVAudioFrameCount(file!.length))
do {
try file!.read(into: buffer!)
} catch {
// problem, do something
}
I looked into AVAudioCompressedBuffer but I do not see how I get the data into
this type of buffer and how to expand this into raw data for manipulation
If it matters, I am programming on OSX (Sierra).
Any advice?
Thank you,
W.
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