fix(count-in): follow the song's meter and its pickup measure - #1029
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The count-in always clicked exactly four beats, so a 3/4 song was counted in 4/4, and a song opening with a pickup (anacrusis) had the pickup enter where the downbeat belonged — putting the player a beat ahead all song. Bar length now comes from the song_timeline beats already on the highway (measure >= 0 marks downbeats), so no new plumbing: the time_signatures map is streamed to plugins rather than stored in the frontend. A first bar shorter than that meter shortens the count by its length — a 1-beat pickup in 4/4 counts "1 2 3" and the music enters on 4. Bar length is the mode of the downbeat gaps, not the first gap, so a pickup's own short gap can't be read as the meter; the beats trailing the last downbeat count as a candidate too, or a song of pickup + one bar offers only the pickup's gap. Pickup shortening is scoped to the song's first bar — a short bar elsewhere is a meter change, and is counted by its own length instead. Songs without beats (pre-chart, minigames, synthetic highways) still get four. Applies to both count-in paths: loop wrap / section practice, and the start-of-song 'Countdown before song' setting. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Signed-off-by: gionnibgud <gionnibgud@gmail.com>
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2 participants
Problem
A user reported the metronome fighting the barlines on a 4/4 piano score
opening with a pickup measure (two eighth notes). Chasing it surfaced the
count-in as an independent bug, in core rather than any plugin.
The count-in clicked exactly four beats, always. Two consequences:
downbeat belonged, so the player came in a beat ahead — for the whole song,
since nothing later corrects the impression.
Fix
Bar length now comes from the
song_timelinebeats already on the highway.Beats carry
measure >= 0on downbeats, so the gap between consecutivedownbeats is the bar length — no new plumbing, which matters because the
frontend never consumes the
time_signaturesWS message at all (it is streamedto plugins only, so making count-in time-signature-aware that way would have
meant new state to load, reset, and keep in sync).
A first bar shorter than that meter is a pickup, and the count is shortened by
its length: a 1-beat pickup in 4/4 counts “1 2 3” and the music enters on 4.
Three details that are load-bearing rather than incidental:
first gap in a pickup song is the pickup, which would then be read as the
meter.
a song of pickup + one bar offers only the pickup’s gap and the count
collapses to it.
else is a meter change (or a truncated final bar); treating one as a pickup
would leave nearly no count-in. Those are counted by their own length, which
is also what a mid-song meter change wants.
Songs with no beats — pre-chart, minigames, synthetic highways — still get
four. Both count-in paths use it: loop wrap / section practice, and the
start-of-song “Countdown before song” setting.
Testing
tests/js/count_in_beats.test.js— 15 new cases: meter (3/4, 4/4, 6/8),pickups of 1 and 2 beats in 4/4 and 3/4, the pickup-plus-one-bar tie, a
mid-song meter change counted as its own bar rather than a pickup, mid-bar
and mid-song-downbeat resumes, seek slop, and every no-beats fallback.
tests/js/loop_restart.test.jsgains acountInBeatsstub — it sandboxesstartCountInandbeginCountnow calls one more helper. Assertionsunchanged.
on four, accents land on the barlines.
Related
The same report also needed two plugin-side fixes, both merged/open separately
— the MusicXML converter was dropping the first full measure’s downbeat label
(got-feedBack/feedBack-plugin-musicxml-import#10) and staffview was accenting
the pickup (got-feedBack/feedBack-plugin-staffview#23). This PR stands on its
own: it affects every instrument, not just notation.
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