函数 av_audio_fifo_drain 

pub unsafe extern "C" fn av_audio_fifo_drain(
    af: *mut AVAudioFifo,
    nb_samples: c_int,
) -> c_int

Drain data from an AVAudioFifo.

Removes the data without reading it.

@param af AVAudioFifo to drain @param nb_samples number of samples to drain @return 0 if OK, or negative AVERROR code on failure