Re: Time measurement

[Lukas-Fabian Moser]

Hi,

Am 14.03.24 um 17:27 schrieb Kieren MacMillan:
> Hi Matthew,
>
> > Is there any easy way to find out the time in seconds from the start of a
> > score to a specified point, corresponding to the timing of the MIDI
> > output?  I can count measures and do math on the tempo, but that's
> > less than ideal in the face of multiple tempo changes.  Another idea would
> > be to just cut the score at the desire point and then measure the length
> > of the MIDI output file.  I can already manually examine the MIDI output,
> > find the desired point in the music, and record its timing, but that's
> > a fair bit of work.
> >
> > I only really need to do this for a few points, a few times, and I just
> > want to know the numbers, not necessarily typeset them.  But a more
> > automated method along the lines of a \midiTime markup that would actually
> > typeset the time to that point automatically, would be fun too.
> “This sounds like a job for… Custom Engraver!!”  :)

It sure does.

\version "2.25.3"

#(set-object-property! 'physicalTime 'translation-type? real?)

Time_measuring_engraver =
#(lambda (context)
   (let
    ((previous-timestep #f)
     (now ZERO-MOMENT)
     (current-tempo #f)
     (elapsed-time 0.0))

    (make-engraver
     ((initialize engraver)
      (ly:context-set-property! context 'physicalTime elapsed-time))
     ((start-translation-timestep engraver)
      (set! now (ly:context-current-moment context))
      (let*
       ((current-delta (- now previous-timestep))
        (current-timespan (/ current-delta current-tempo)))
       (set! elapsed-time (+ elapsed-time (* 60 current-timespan))))
      (ly:context-set-property! context 'physicalTime elapsed-time))
     ((stop-translation-timestep engraver)
      (set! previous-timestep now)
      (set! current-tempo (ly:context-property context
'tempoWholesPerMinute))))))

\layout {
  \context {
    \Score
    \consists #Time_measuring_engraver
    tempoWholesPerMinute = \musicLength 1*15 % LilyPond's default
  }
}

displayPhysicalTime = \applyContext
#(lambda (context)
   (ly:message "Elapsed time: ~as" (ly:context-property context
'physicalTime)))

{
  \tempo 4 = 120
  \tuplet 3/2 { a4 \displayPhysicalTime a a } \displayPhysicalTime a2
  \displayPhysicalTime
  \tempo 4 = 80
  a1 \displayPhysicalTime
}

Look at LilyPond's log.

It would be absolutely possible to also let this number be typeset (e.g.
as a TextMark), but this needs a dedicated engraver again as far as I
can see: They form the link between time-dependent context information
and grobs. A general \midiTime markup can't work conceptually, I think,
as markups may live independently of any music.

Lukas

Lukas