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Re: old mtcoreaudio code doesn't work now


On Jan 8, 2008, at 4:08 PM, dudley ackerman wrote:


On Jan 8, 2008, at 3:32 PM, dudley ackerman wrote:
<snip>
is it possible that we used to be able specify that we wanted data as 16 bit frames and we can't do that in the latest version of mtcoreaudio?

we used this setup for the app side specification for source of output and destination of input:
AudioStreamBasicDescription shtoomDescription;
shtoomDescription.mSampleRate = [self sampleRate];
shtoomDescription.mFormatID = kAudioFormatLinearPCM;
shtoomDescription.mFormatFlags = kLinearPCMFormatFlagIsPacked | kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsBigEndian | kAudioFormatFlagIsNonInterleaved;
shtoomDescription.mBytesPerFrame = sizeof(SInt16);
shtoomDescription.mFramesPerPacket = 1;
shtoomDescription.mBytesPerPacket = sizeof(SInt16);
shtoomDescription.mChannelsPerFrame = 1;
shtoomDescription.mBitsPerChannel = 16;
shtoomDescription.mReserved = 0;

do i now have to expect Float32 frames and have to convert that to 16bit integer frames in my own code.
i'm sure that is my problem -- i just had to stare at the code long enough to see it. 

ok, so maybe i am not so sure.
the old code used the mBytesPerFrame where the new code just uses '2'.

so, what is the meaning of this snippet in MTConversionBuffer.m:
	srcFrames = ((srcFrames * 2) / srcChans) / sizeof(Float32);
	dstFrames = ((dstFrames * 2) / dstChans) / sizeof(Float32);

what is Float32 in the conversion and what is 16 bit?

the above doesn't actually appear in my code (either the current release or previous one). furthermore, MTCoreAudio has always been *only* Float32 everywhere that deals with samples.

and while i am here, how about this snippet in the same method in the old code:
BOOL srcInterleaved = !(srcDescription.mFormatFlags & kAudioFormatFlagIsNonInterleaved);
BOOL dstInterleaved = !(dstDescription.mFormatFlags & kAudioFormatFlagIsNonInterleaved);

audioBuffer = [[MTAudioBuffer alloc] initWithCapacityFrames:totalBufferFrames channels:srcChans interleaved:srcInterleaved];


now, in the latest version of mtcoreaudio i see:
conversionChannels = MIN ( srcChans, dstChans );

audioBuffer = [[MTAudioBuffer alloc] initWithCapacityFrames:totalBufferFrames channels:conversionChannels];


doesn't interleaving matter, anymore?

this also doesn't appear in either the current or previous release of MTCoreAudio. however, interleaving doesn't matter* -- the right thing will happen when AudioBufferLists are copied from or to the buffers.

if you're getting static, trying to use integer samples instead of Float32 would definitely be a cause.

* it doesn't matter (except possibly for performance when there are mismatches) in the code i actually released. however, i have no idea how the code you're using, as modified by others in ways unknown to me, will behave.

-mike

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References: 
 >Re: old mtcoreaudio code doesn't work now (From: dudley ackerman <email@hidden>)
 >Re: old mtcoreaudio code doesn't work now (From: Michael Thornburgh <email@hidden>)
 >Re: old mtcoreaudio code doesn't work now (From: dudley ackerman <email@hidden>)
 >Re: old mtcoreaudio code doesn't work now (From: Michael Thornburgh <email@hidden>)
 >Re: old mtcoreaudio code doesn't work now (From: Michael Thornburgh <email@hidden>)
 >Re: old mtcoreaudio code doesn't work now (From: dudley ackerman <email@hidden>)
 >Re: old mtcoreaudio code doesn't work now (From: dudley ackerman <email@hidden>)



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