inputs
The number of inputs. If unspecified, it defaults to 2.//输入的数量,如果没有指明,默认为2.
duration
How to determine the end-of-stream.//决定了流的结束
longest
The duration of the longest input. (default)//最长输入的持续时间
shortest
The duration of the shortest input.//最短输入的持续时间
first
The duration of the first input.//第一个输入的持续时间
dropout_transition
The transition time, in seconds, for volume renormalization when an input stream ends. The default value is 2 seconds.
//指一个输入流结束时音量从正常到无声渐止效果,默认为2秒