_engine = [[AVAudioEngine alloc] init];
    AVAudioMixerNode *resamplerNode = [[AVAudioMixerNode alloc] init];
    [_engine attachNode: resamplerNode];
    [_engine connect:_engine.inputNode to:resamplerNode format:[_engine.inputNode inputFormatForBus:0]];
    [resamplerNode installTapOnBus:0
                        bufferSize:512
                            format:_inputFormat
                             block:^(AVAudioPCMBuffer * _Nonnull buffer, AVAudioTime * _Nonnull when) {
        printf("tap! %lf\n", [_engine.inputNode inputFormatForBus:0].sampleRate);
    }];