ios - 如何使用 AudioConverterFillComplexBuffer iOS 将 AAC 压缩帧解码为 PCM

Question

我想在我的应用程序中实现 SIP 调用，我需要解决的第一个问题是将音频从带有 ADTS header 的压缩 AAC 格式转换为线性 PCM。

我的输入数据是具有不同帧大小的 ADTS 帧的 NSArray。每一帧都是 NSMutableData 类型。每帧都具有相同的格式和采样率，唯一不同的是帧大小。

我尝试实现 Igor Rotaru 为 this issue 建议的示例代码, 但无法使其正常工作。

现在我的代码看起来像这样。首先，我配置 AudioConverter:

- (void)configureAudioConverter {
    AudioStreamBasicDescription inFormat;
    memset(&inFormat, 0, sizeof(inFormat));
    inputFormat.mBitsPerChannel = 0;
    inputFormat.mBytesPerFrame = 0;
    inputFormat.mBytesPerPacket = 0;
    inputFormat.mChannelsPerFrame = 1;
    inputFormat.mFormatFlags = kMPEG4Object_AAC_LC;
    inputFormat.mFormatID = kAudioFormatMPEG4AAC;
    inputFormat.mFramesPerPacket = 1024;
    inputFormat.mReserved = 0;
    inputFormat.mSampleRate = 22050;

    AudioStreamBasicDescription outputFormat;
    memset(&outputFormat, 0, sizeof(outputFormat));
    outputFormat.mSampleRate       = inputFormat.mSampleRate;
    outputFormat.mFormatID         = kAudioFormatLinearPCM;
    outputFormat.mFormatFlags      = kLinearPCMFormatFlagIsSignedInteger;
    outputFormat.mBytesPerPacket   = 2;
    outputFormat.mFramesPerPacket  = 1;
    outputFormat.mBytesPerFrame    = 2;
    outputFormat.mChannelsPerFrame = 1;
    outputFormat.mBitsPerChannel   = 16;
    outputFormat.mReserved         = 0;

    AudioClassDescription *description = [self
                                      getAudioClassDescriptionWithType:kAudioFormatMPEG4AAC
                                      fromManufacturer:kAppleSoftwareAudioCodecManufacturer];

    OSStatus status =  AudioConverterNewSpecific(&inputFormat, &outputFormat, 1, description, &_audioConverter);

    if (status != 0) {
        printf("setup converter error, status: %i\n", (int)status);
    }
}

之后我写了回调函数:

struct MyUserData {
    UInt32 mChannels;
    UInt32 mDataSize;
    const void* mData;
    AudioStreamPacketDescription mPacket;
};

OSStatus inInputDataProc(AudioConverterRef inAudioConverter,
                         UInt32 *ioNumberDataPackets,
                         AudioBufferList *ioData,
                         AudioStreamPacketDescription **outDataPacketDescription,
                         void *inUserData)
{
    struct MyUserData* userData = (struct MyUserData*)(inUserData);

    if (!userData->mDataSize) {
        *ioNumberDataPackets = 0;
        return kNoMoreDataError;
    }

    if (outDataPacketDescription) {
        userData->mPacket.mStartOffset = 0;
        userData->mPacket.mVariableFramesInPacket = 0;
        userData->mPacket.mDataByteSize = userData->mDataSize;
        *outDataPacketDescription = &userData->mPacket;
    }

    ioData->mBuffers[0].mNumberChannels = userData->mChannels;
    ioData->mBuffers[0].mDataByteSize = userData->mDataSize;
    ioData->mBuffers[0].mData = (void *)userData->mData;

    // No more data to provide following this run.
    userData->mDataSize = 0;

    return noErr;
}

我解码帧的函数如下所示:

- (void)startDecodingAudio {
    if (!_converterConfigured){
        return;
    }

    while (true){
        if ([self hasFramesToDecode]){
            struct MyUserData userData = {1, (UInt32)_decoderBuffer[_currPosInDecoderBuf].length, _decoderBuffer[_currPosInDecoderBuf].bytes};

            uint8_t *buffer = (uint8_t *)malloc(128 * sizeof(short int));
            AudioBufferList decBuffer;
            decBuffer.mNumberBuffers = 1;
            decBuffer.mBuffers[0].mNumberChannels = 1;
            decBuffer.mBuffers[0].mDataByteSize = 128 * sizeof(short int);
            decBuffer.mBuffers[0].mData = buffer;

            UInt32 numFrames = 128;

            AudioStreamPacketDescription outPacketDescription;
            memset(&outPacketDescription, 0, sizeof(AudioStreamPacketDescription));
            outPacketDescription.mDataByteSize = 128;
            outPacketDescription.mStartOffset = 0;
            outPacketDescription.mVariableFramesInPacket = 0;

            OSStatus status = AudioConverterFillComplexBuffer(_audioConverter,
                                                              inInputDataProc,
                                                              &userData,
                                                              &numFrames,
                                                              &decBuffer,
                                                              &outPacketDescription);

            NSError *error = nil;

            if (status == kNoMoreDataError) {
                NSLog(@"%u bytes decoded", (unsigned int)decBuffer.mBuffers[0].mDataByteSize);
                [_decodedData appendData:[NSData dataWithBytes:decBuffer.mBuffers[0].mData length:decBuffer.mBuffers[0].mDataByteSize]];
                _currPosInDecoderBuf += 1;
            } else {
                error = [NSError errorWithDomain:NSOSStatusErrorDomain code:status userInfo:nil];
            }
        } else {
            break;
        }
    }
}

每次，AudioConverterFillComplexBuffer 都会返回状态 1852797029，根据 Apple API，这是 kAudioCodecIllegalOperationError。如果有人成功转换为此类格式，请分享一些示例或建议。

Answer 1

最后，我用 StreamingKit 库解码了我的字节(可以找到原始存储库 here)。