Re: ExtAudioFileRead performance
Re: ExtAudioFileRead performance
- Subject: Re: ExtAudioFileRead performance
- From: William Stewart <email@hidden>
- Date: Thu, 1 Oct 2009 19:16:34 -0700
On Oct 1, 2009, at 10:45 AM, Dominic Feira wrote:
I'm getting some really poor performance with ExtAudioFileRead
sometimes. While reading audio from a m4a with Apple Lossless in
it, it sometimes takes an extremely long time to complete the read.
Typically it takes on 0.000002 seconds to complete the read. Then
out of nowhere it takes approximate 0.4 seconds to complete the
read. The reads are for 256 samples of audio at a time. Perhaps
this should be larger?
Yes
The only thing that I can think of is disk contention, but at 0.4
seconds that seems like a long time even for disk contention.
Does anybody have any ideas why ExtAudioFileRead could be so slow?
Apple Lossless is packetised into data chunks that are 4096 samples
long. So, probably what is happening is that you are reading 1 packet,
decoding it (you have 4096 samples), and ExtAudioFile returns you your
256 samples. Then you read again, it already has enough decoded data,
so it just passes you back the next 256 samples, and again, until
eventually it runs out and has to actually go and read some more and
decode it, then it starts again.
But really, this is a very poor way of interacting with the file
system. You should be reading larger chunks when you have to go and
read.
Bill
Dominic Feira / Code Monkey / Ambrosia Software, Inc. -- http://www.AmbrosiaSW.com
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