函数 av_channel_description 

pub unsafe extern "C" fn av_channel_description(
    buf: *mut c_char,
    buf_size: usize,
    channel: AVChannel,
) -> c_int

Get a human readable string describing a given channel.

@param buf pre-allocated buffer where to put the generated string @param buf_size size in bytes of the buffer. @param channel the AVChannel whose description to get @return amount of bytes needed to hold the output string, or a negative AVERROR on failure. If the returned value is bigger than buf_size, then the string was truncated.