Editing Time mark engraver

When working with LilyPond’s MIDI output it can be tedious to find the exact ‘elapsed time from the start of the score to an arbitrary point’ – especially when the music contains multiple tempo changes. Counting measures and doing tempo math is error-prone; inspecting the MIDI file manually is possible but time consuming.

This snippets introduces a Scheme engraver that allows you to insert time marks directly into the music. At any point in the score you can add <code>\timeMark</code>, and LilyPond computes the elapsed time up to that position and displays it (for example, ‘2m15s’).

This is useful when you need to

* align score events with audio or video cues,
* locate timestamps for MIDI-driven playback or mockups,
* find “time since start” at a few musical key positions without counting or math, or
* work reliably across complex tempo maps (rit., accel., metric modulations, etc.).

''Upgrade notice'': This snippet must be updated with the {{Convert-ly-devel}} script if used with a LilyPond version newer than 2.24.

<lilypond version="2.24">
% LSR source: https://lists.gnu.org/archive/html/lilypond-user/2024-03/msg00127.html
% LSR credits: 2024 - Jean Abou Samra

#(define (Elapsed_time_engraver context)
   (define (format-time seconds) ; example: 2m15s
     (let ((minutes (euclidean-quotient seconds 60))
           (rest (euclidean-remainder seconds 60)))
       (string-append (if (zero? minutes) "" (format #f "~am" minutes))
                      (format #f "~as" (round rest)))))

   (let ((wholes-per-minute 15)
         (last-time ZERO-MOMENT)
         (total-time 0)
         (marks '()))
     (make-engraver
      ((process-music engraver)
       (let* ((new-time (ly:context-current-moment context))
              (time-delta (ly:moment-main
                           (ly:moment-sub new-time last-time)))
              (new-wholes-per-minute
               (and=> (ly:context-property context
                                           'tempoWholesPerMinute #f)
                      ly:moment-main)))
         (set! total-time
               (+ total-time (* 60 (/ time-delta wholes-per-minute))))
         (set! last-time new-time)
         (when new-wholes-per-minute
           (set! wholes-per-minute new-wholes-per-minute))))

      (acknowledgers
       ((text-mark-interface engraver grob source-engraver)
        (set! marks (cons grob marks))))

      ((process-acknowledged engraver)
       (for-each (lambda (grob)
                   (when (assq-ref (ly:grob-property grob 'details)
                                   'time-mark)
                     (ly:grob-set-property!
                      grob 'text (format-time total-time))))
                 marks)
       (set! marks '())))))


\layout {
  \context {
    \Score
    \consists #Elapsed_time_engraver
  }
}

% The argument of the `\textEndMark` here is just a placeholder
% that the engraver replaces with a time stamp (because the
% `time-mark` subproperty is set).
timeMark = \tweak details.time-mark ##t
           \tweak color "red"
           \textEndMark ""

{
  c'1 | \timeMark
  \tempo 4 = 120 c'4 8. 16 2 | \timeMark
  \tempo 4 = 180 \repeat unfold 4 c'2 | \timeMark
  \repeat unfold 180 c'4 | \timeMark
}
</lilypond>

[[Category:Automatic notation]]
[[Category:Contexts and engravers]]
[[Category:Editorial annotations]]
[[Category:Midi]]
[[Category:Scheme]]
[[Category:Snippet]]