I hope this list is alive- I haven't seen anything since I signed up 24 hours
ago!
I am using ExtAudioFile API's to extract the data from sound files (we publish
a scientific data analysis application). I can open a file and read the data
just fine. Core Audio makes it pretty easy to do that with a large variety of
sound files.
I'm doing this on a 5k iMac running OS X 10.10.3. Writing in C++, not Objective
C++, in case that's relevant.
BUT...
I can't seek. I am trying to use this:
SInt64 seekFrames = 0;
if (_startAndEndSet)
{
seekFrames = _starttime*formatDescription.mSampleRate;
seekFrames = std::max(SInt64(0), seekFrames);
if (seekFrames >= fileFrames)
{
_error = SYNERR; // TODO: better
errors
return;
}
if (seekFrames > 0)
{
_error = ExtAudioFileSeek(_audioFileRef, seekFrames);
if (_error)
return;
}
...
I always get kExtAudioFileError_InvalidSeek no matter what value seekFrames
has.
At least I get a documented error code!
I would also like to get at some of the metadata, like the channel layout. For
that I use code like this:
Boolean writable;
AudioChannelLayout * filechannelLayout;
_error = ExtAudioFileGetPropertyInfo (_audioFileRef,
kExtAudioFileProperty_FileChannelLayout, &datasize, &writable);
filechannelLayout = reinterpret_cast<AudioChannelLayout *>(malloc(92));
_error = ExtAudioFileGetProperty(_audioFileRef,
kExtAudioFileProperty_FileChannelLayout, &datasize, filechannelLayout);
if (_error)
return;
std::cerr << "ChannelLayout struct basic size =" <<
sizeof(AudioChannelLayout) << "; real size:" << datasize << std::endl;
std::cerr << "Channel layout for file:" <<
ChannelLayoutTagToString(filechannelLayout->mChannelLayoutTag) << std::endl;
free(filechannelLayout);
For a .mp4 file, I get back the kAudioChannelLayoutTag_MPEG_5_1_D tag. That's
good!
For an AIFF file with four channels, I get back the
kAudioChannelLayoutTag_UseChannelDescriptions tag. That's OK- I can dump the
file and I see a CHAN chunk with what appear to be good channel descriptors.
But ExtAudioFileGetPropertyInfo tells me that the data size is 12 bytes (just
enough for the three basic members of the structure, but not enough for the
array of channel descriptors).
I've been beating my head on this wall for two days...
-John Weeks
WaveMetrics, Inc.
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