我已经设置了一个类,在给定输入和输出AudioStreamBasicDescription
的情况下将音频从一种格式转换为另一种格式。当我将线性PCM从麦克风转换为iLBC时,当我从AudioUnitRender
函数给出1024个数据包时,它会工作并给我6个数据包。然后我通过UDP将这226个字节发送到在不同设备上运行的同一个应用程序。问题是,当我使用相同的类转换回线性PCM以提供音频单元输入时,AudioConverterFillComplexBuffer
函数不提供1024个数据包,它给出960 ...这意味着音频单元输入期望4096字节(立体声为2048 x 2),但我只能给它3190左右,所以它听起来真的很破碎和扭曲......
如果我提供AudioConverter
1024个LinearPCM数据包,转换为iLBC,转换回LinearPCM,我肯定会再次获得1024个数据包吗?
音频转换器功能:
-(void) doConvert {
// Start converting
if (converting) return;
converting = YES;
while (true) {
// Get next buffer
id bfr = [buffers getNextBuffer];
if (!bfr) {
converting = NO;
return;
}
// Get info
NSArray* bfrs = ([bfr isKindOfClass:[NSArray class]] ? bfr : @[bfr]);
int bfrSize = 0;
for (NSData* dat in bfrs) bfrSize += dat.length;
int inputPackets = bfrSize / self.inputFormat.mBytesPerPacket;
int outputPackets = (inputPackets * self.inputFormat.mFramesPerPacket) / self.outputFormat.mFramesPerPacket;
// Create output buffer
AudioBufferList* bufferList = (AudioBufferList*) malloc(sizeof(AudioBufferList) * self.outputFormat.mChannelsPerFrame);
bufferList -> mNumberBuffers = self.outputFormat.mChannelsPerFrame;
for (int i = 0 ; i < self.outputFormat.mChannelsPerFrame ; i++) {
bufferList -> mBuffers[i].mNumberChannels = 1;
bufferList -> mBuffers[i].mDataByteSize = 4*1024;
bufferList -> mBuffers[i].mData = malloc(bufferList -> mBuffers[i].mDataByteSize);
}
// Create input buffer
AudioBufferList* inputBufferList = (AudioBufferList*) malloc(sizeof(AudioBufferList) * bfrs.count);
inputBufferList -> mNumberBuffers = bfrs.count;
for (int i = 0 ; i < bfrs.count ; i++) {
inputBufferList -> mBuffers[i].mNumberChannels = 1;
inputBufferList -> mBuffers[i].mDataByteSize = [[bfrs objectAtIndex:i] length];
inputBufferList -> mBuffers[i].mData = (void*) [[bfrs objectAtIndex:i] bytes];
}
// Create sound data payload
struct SoundDataPayload payload;
payload.data = inputBufferList;
payload.numPackets = inputPackets;
payload.packetDescriptions = NULL;
payload.used = NO;
// Convert data
UInt32 numPackets = outputPackets;
OSStatus err = AudioConverterFillComplexBuffer(converter, acvConverterComplexInput, &payload, &numPackets, bufferList, NULL);
if (err)
continue;
// Check how to output
if (bufferList -> mNumberBuffers > 1) {
// Output as array
NSMutableArray* array = [NSMutableArray arrayWithCapacity:bufferList -> mNumberBuffers];
for (int i = 0 ; i < bufferList -> mNumberBuffers ; i++)
[array addObject:[NSData dataWithBytes:bufferList -> mBuffers[i].mData length:bufferList -> mBuffers[i].mDataByteSize]];
// Save
[convertedBuffers addBuffer:array];
} else {
// Output as data
NSData* newData = [NSData dataWithBytes:bufferList -> mBuffers[0].mData length:bufferList -> mBuffers[0].mDataByteSize];
// Save
[convertedBuffers addBuffer:newData];
}
// Free memory
for (int i = 0 ; i < bufferList -> mNumberBuffers ; i++)
free(bufferList -> mBuffers[i].mData);
free(inputBufferList);
free(bufferList);
// Tell delegate
if (self.convertHandler)
//dispatch_async(dispatch_get_main_queue(), self.convertHandler);
self.convertHandler();
}
}
转换为iLBC时的格式:
// Get input format from mic
UInt32 size = sizeof(AudioStreamBasicDescription);
AudioStreamBasicDescription inputDesc;
AudioUnitGetProperty(self.ioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &inputDesc, &size);
// Set output stream description
size = sizeof(AudioStreamBasicDescription);
AudioStreamBasicDescription outputDescription;
memset(&outputDescription, 0, size);
outputDescription.mFormatID = kAudioFormatiLBC;
OSStatus err = AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &size, &outputDescription);
从iLBC转换时的格式:
// Set input stream description
size = sizeof(AudioStreamBasicDescription);
AudioStreamBasicDescription inputDescription;
memset(&inputDescription, 0, size);
inputDescription.mFormatID = kAudioFormatiLBC;
AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &size, &inputDescription);
// Set output stream description
UInt32 size = sizeof(AudioStreamBasicDescription);
AudioStreamBasicDescription outputDesc;
AudioUnitGetProperty(unit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &outputDesc, &size);
答案 0 :(得分:1)
您必须使用中间缓冲区从足够的传入数据包中保存足够的字节,以完全匹配音频单元输入所请求的数量。取决于压缩格式的任何一个UDP数据包是否正确大小将无法正常工作。
AudioConverter可以缓冲样本并根据压缩格式更改数据包大小。