声道数。 0: Defined in AOT Specifc Config 1: 1 channel : front - center 2 : 2 channels : front - left, front - right 3 : 3 channels : front - center, front - left, front - right 4 : 4 channels : front - center, front - left, front - right, back - center 5 : 5 channels : front - center, front - left, front - right, back - left, back - right 6 : 6 channels : front - center, front - left, front - right, back - left, back - right, LFE - channel 7 : 8 channels : front - center, front - left, front - right, side - left, side - right, back - left, back - right, LFE - channel 8 - 15 : Reserved front - center：中置声道

front - left：左声道

front - right：右声道

back - left：后置左

back - right：后置右

side - left：侧置左

side - right：侧置右

LFE - channel：低频声道

音频通道也在ffmpeg的AVStream中：

streams[audio]->codecpar->channels

audio:帧索引