Duration of an audio sound or time series object as a Quantity
与 .wl 参考的差异： `Duration` of a `Video`, `DateInterval` or `Play`
Duration[expr]
Duration[expr, unit]
ts = TimeSeries[{2, 1, 6, 5, 7, 4}, {{1, 2, 5, 10, 12, 15}}]; Duration[ts]
→ Quantity[14, Seconds]