Hello Michael,
I've tried sending you this email directly, but I keep getting mail
delivery failures. So I'm trying to reach you via the CoreAudio list.
I've spent some time with MTCoreAudio, trying to understand how it
works (without much knowledge on CoreAudio), and well, it's great!
I have found one inconsistency though (or perhaps it's missing
knowledge on my side)...
I have set up my device (standard line-in), got it's first stream
from the streams array, and set the stream description to my desired
format (16 bit signed integer 2 channel little endian).
To verify that the change to the stream was applied correctly, I'm
checking my device's delegate
audioDeviceStreamDescriptionDidChange:forChannel:forDirection and
outputting some info there.
Now, If output the information via
MTCoreAudioStreamDescription *streamDesc [device
streamDescriptionForChannel:theChannel forDirection:theDirection];
I'm getting a wrong stream description (not the one I did set). That
was my first choice as it contains exactly the same parameters as
supplied to the delegate.
But if I get the description using
MTCoreAudioStream *stream = [[device
streamsForDirection:kMTCoreAudioDeviceRecordDirection] objectAtIndex:0];
MTCoreAudioStreamDescription *streamDesc = [stream
streamDescriptionForSide:kMTCoreAudioStreamPhysicalSide];
I get the correct one, as I set it.
Now, which information is right? What will the device output?
I am also confused about the inInputTime->mSampleTime for my input
device IO procedure. For the first buffer, it is returning a negative
number. Here's a short log for the first few buffers:
-237.000000
4173.000000
8583.000000
12993.000000
The difference between the buffers is always 4410, what matches the
devices buffer size I'm setting with [inputDevice
setDeviceBufferSizeInFrames:4410];
But was does the negative value actually mean? Shall I ignore the
first buffer or does it contain valid data?
I would really appreciate some help. Best regards
Mark
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