The s6-tai64ndiff program

s6-tai64ndiff acts as a filter, reading from stdin and writing to stdout. It expects every line of its input to begin with a TAI64N timestamp. It replaces this timestamp with a prefix showing the time difference between this line and the previous line.

Interface

     s6-tai64ndiff

s6-tai64ndiff exits 0 when it sees the end of stdin. If there's an unfinished line, s6-tai64ndiff processes it and writes it before exiting.
The prefix it prints is of the form [ seconds.microseconds ], in decimal. It can be interpreted as a fixed-point decimal number of seconds that elapsed between the timestamp on the previous line and the timestamp on the current line.
If the difference isn't defined, seconds and microseconds are just whitespace. The difference is not defined on the first line of stdin or on non-timestamped lines. Following non-timestamped lines, the difference may not be accurate.

Notes

The typical use case of s6-tai64ndiff is to read files that have been filtered through s6-tai64n, or log files that have been produced by s6-log with the t directive.
The difference is a signed number. Negative numbers probably indicate a backwards clock jump, which is a bad thing to have on a system.