iOS convert audio sample rate from 16 kHz to 8 kHz - ios

Question

I tried to convert PCM audio from 16kHz to 8kHz, just sample rate, no format change, the flow looks simple but I kept getting kAudioConverterErr_InvalidInputSize ("insz") from calling AudioConverterFillComplexBuffer. My input audio sample size is 320 bytes, the result is supposed to be 160 bytes but I just got 144 bytes in my output buffer. have been pulling my hair off for the last couple hours. Is there any setting wrong?
static AudioConverterRef PCM8kTo16kConverterRef;
- (instancetype)init {
self = [super init];
if (self) {
[self initConverter];
}
return self;
}
-(void)initConverter{
AudioStreamBasicDescription PCM8kDescription = {0};
PCM8kDescription.mSampleRate = 8000.0;
PCM8kDescription.mFormatID = kAudioFormatLinearPCM;
PCM8kDescription.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked | kAudioFormatFlagsNativeEndian;
PCM8kDescription.mBitsPerChannel = 8 * sizeof(SInt16);
PCM8kDescription.mChannelsPerFrame = 1;
PCM8kDescription.mBytesPerFrame = sizeof(SInt16) * PCM8kDescription.mChannelsPerFrame;
PCM8kDescription.mFramesPerPacket = 1;
PCM8kDescription.mBytesPerPacket = PCM8kDescription.mBytesPerFrame * PCM8kDescription.mFramesPerPacket;
AudioStreamBasicDescription PCM16kDescription = {0};
PCM16kDescription.mSampleRate = 16000.0;
PCM16kDescription.mFormatID = kAudioFormatLinearPCM;
PCM16kDescription.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked | kAudioFormatFlagsNativeEndian;
PCM16kDescription.mBitsPerChannel = 8 * sizeof(SInt16);
PCM16kDescription.mChannelsPerFrame = 1;
PCM16kDescription.mBytesPerFrame = sizeof(SInt16) * PCM16kDescription.mChannelsPerFrame;
PCM16kDescription.mFramesPerPacket = 1;
PCM16kDescription.mBytesPerPacket = PCM16kDescription.mBytesPerFrame * PCM16kDescription.mFramesPerPacket;
OSStatus status = AudioConverterNew(&PCM16kDescription, &PCM8kDescription, &converterRef);
}
OSStatus inInputDataProc(AudioConverterRef inAudioConverter, UInt32 *ioNumberDataPackets, AudioBufferList *ioData, AudioStreamPacketDescription **outDataPacketDescription, void *inUserData)
{
AudioBufferList audioBufferList = *(AudioBufferList *)inUserData;
ioData->mBuffers[0].mData = audioBufferList.mBuffers[0].mData;
ioData->mBuffers[0].mDataByteSize = audioBufferList.mBuffers[0].mDataByteSize;
return noErr;
}
- (NSData *)testSample:(NSData *)inAudio {
NSMutableData *ddd = [inAudio mutableCopy];
AudioBufferList inAudioBufferList = {0};
inAudioBufferList.mNumberBuffers = 1;
inAudioBufferList.mBuffers[0].mNumberChannels = 1;
inAudioBufferList.mBuffers[0].mDataByteSize = (UInt32)[ddd length];
inAudioBufferList.mBuffers[0].mData = [ddd mutableBytes];
uint32_t bufferSize = (UInt32)[inAudio length] / 2;
uint8_t *buffer = (uint8_t *)malloc(bufferSize);
memset(buffer, 0, bufferSize);
AudioBufferList outAudioBufferList;
outAudioBufferList.mNumberBuffers = 1;
outAudioBufferList.mBuffers[0].mNumberChannels = 1;
outAudioBufferList.mBuffers[0].mDataByteSize = bufferSize;
outAudioBufferList.mBuffers[0].mData = buffer;
UInt32 ioOutputDataPacketSize = bufferSize;
OSStatus ret = AudioConverterFillComplexBuffer(converterRef, inInputDataProc, &inAudioBufferList, &ioOutputDataPacketSize, &outAudioBufferList, NULL) ;
NSData *data = [NSData dataWithBytes:outAudioBufferList.mBuffers[0].mData length:outAudioBufferList.mBuffers[0].mDataByteSize];
free(buffer);
return data;
}

Answer 1

There are two problems:
your AudioConverterComplexInputDataProc isn't setting ioNumberDataPackets:
*ioNumberDataPackets = audioBufferList.mBuffers[0].mDataByteSize/2;
ioOutputDataPacketSize is supposed to be the output buffer capacity in packets/frames, not bytes, so shouldn't you divide by 2?