Re: ExtAudioFile woes
Re: ExtAudioFile woes
- Subject: Re: ExtAudioFile woes
- From: John Weeks <email@hidden>
- Date: Thu, 04 Jun 2015 11:00:33 -0700
Thanks, Christian.
> On 03 Jun 2015, at 5:21 pm, Christian Rober <email@hidden> wrote:
>
> Hi John,
>
> Without trying this out, here are some quick thoughts that may help (I apologize if you have already tried these):
>
> 1) What is value range/type of _starttime? Is it in seconds? Milliseconds? CPU time? I would make sure that it is in seconds, because a really large millisecond value may generate an offset beyond the end of a small file.
Yeah- _starttime is in seconds, and I can't get it to work even when I set the frameOffset input to literal "1".
> 2) I would use ExtAudioFileTell() as a sanity check before you call this code. Print out the value, it should be 0 at first, if you haven't read from it already.
I did that, too. I gave zero.
> 3) Have you been reading from the file? Just like Unix open and its corresponding file descriptor, an ExtAudioFileRead (+Async) on this file will advance the position in the file that a seek uses. In other words, since there is no pread() equivalent in the ExtAudioFile framework, all reads seek, and you may already be at or near the end.
No, I do this just before I go into my reading loop. The reading loop works great.
> 4) In terms of the ChannelDescription issue... that is very perplexing. I did see this comment in the documentation which confuses me:
>
> When reading, the specified layout overrides the one read from the file, if one is present in the file.
>
> Maybe the mp4 file does not have a ChannelDescription,
I think that's correct- for the mp4 file I just get a tag giving the name of a particular 5.1 format, and that name implies a channel layout.
> so it reads that description correctly, but the AIFF has a ChannelDescription, as you described by cracking the file open, so you end up inadvertently creating a bogus CD. What is really confusing, is why would a get property overwrite anything?!?
I think you can use ExtAudioFile to convert LPCM to various formats and write the coded audio to a file. But I don't need that- I just want to read the channel layout description that's already in the file!
-John Weeks
WaveMetrics, Inc.
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