Re: Subscription problem
Re: Subscription problem
- Subject: Re: Subscription problem
- From: Steven Winston <email@hidden>
- Date: Tue, 18 May 2010 16:25:46 +0200
Hi Juan,
The only way that I'm aware of to make use of the hardware's decoder
is to utilize AudioQueueServices Offline Renderer. I'm a little
confused by what you're doing. It's admittedly a little weird to
write a 6 minute MP3 to PCM directly in memory. That's a lot of
memory, and probably going to be a waste unless you're doing something
that requires the entire file being open, I'm a little confused as to
what you're after.
What I'd recommend, for 99% of the cases out there, use ExtAudioFile
to read the file and convert from MP3 to PCM, as you start to get the
PCM, work on it, then play it out with RemoteIO. This way your using
the software MP3 (plenty fast, and always performs uniformly), and
you're getting a smaller amount of bufferspace and not having to worry
about a really large PCM file being held in RAM.
Thanks,
Steve
On Mon, May 17, 2010 at 11:58 PM, Juan Pertierra <email@hidden> wrote:
> Hello,
>
> I am trying to decode an MP3 into PCM directly into memory using the
> MP3 decoder hardware in the iPad. I have started with the
> iPhoneExtAudioFileConvert example, which sets the client data format
> to 16-bit PCM and uses ExtAudioFileRead to read and do the conversion
> on the fly(if i understand correctly).
>
> This works but even after pre-allocating all the memory for the PCM
> file, it takes about 17-20 seconds to convert a 6minute MP3 file.
>
> Is this the best MP3 decoding performance? Or is there a faster
> method? I noticed that getting the
> kAudioConverterPropertyCanResumeFromInterruption returns an error -50,
> I think this means hardware decoding is not available which sounds
> like I am doing something wrong. Perhaps there is another way?
>
> I need to decode the entire file at once.
>
> I also tried the audioqueue offline render services example but that
> takes even longer, at least twice as long.
>
> Thanks,
> Juan
>
> PS: Apologies if this gets posted multiple times, I've had problems posting.
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