时间数据与R互补

有以下数据框

> start_time <- c("11:23","16:21","18:57","22:00")
> end_time <- c("11:33","16:23","19:03","22:05")
> vol <- c("red","green","blue","black")
> x <- data.frame(start_time,end_time,vol)
> x
  start_time end_time   vol
1      11:23    11:33   red
2      16:21    16:23 green
3      18:57    19:03  blue
4      22:00    22:05 black

我想按如下方式转换此数据帧。

> time <- c("11:23","11:24","11:25","16:21","16:22","16:23","16:24","18:57","18:58","18:59","19:00","19:01","22:00","22:01","22:02")
> vol <- c("red","red","red","green","green","green","green","blue","blue","blue","blue","blue","black","black","black")
> y <- data.frame(time,vol)
> y
    time   vol
1  11:23   red
2  11:24   red
3  11:25   red
4  16:21 green
5  16:22 green
6  16:23 green
7  16:24 green
8  18:57  blue
9  18:58  blue
10 18:59  blue
11 19:00  blue
12 19:01  blue
13 22:00 black
14 22:01 black
15 22:02 black

从头到尾每隔1分钟添加一次记录。 R有可能吗? 谢谢