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[SyncTrack] is a .chart file’s second section. It holds the chart’s tempo markers, which decide when each tick plays, and its time signatures:

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Tempo markers

A tempo marker sets the tempo from its tick to the next tempo marker:
  • The tempo is in thousandths of a beat per minute: B 120000 is 120 BPM, and B 150325 is 150.325 BPM.
  • Required: a tempo that is a whole number from 1 to 4294967295.
  • Required: one tempo marker at most at a tick.

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Time signatures

A time signature sets the meter from its tick to the next time signature:
  • The numerator is the number of notes in a measure, of the value the denominator gives.
  • The exponent gives the denominator, 2 to the power of the exponent, so TS 6 3 is 6/8: six eighth notes a measure. Without an exponent, the denominator is 4.
  • Required: a numerator from 1 to 4294967295, and an exponent from 0 to 31.
  • Time signatures only change the lines that appear throughout the chart during gameplay, at each measure and between them. They have no influence on the notes themselves.
  • A beat is a quarter note whatever the time signature, so a measure of 6/8 is three beats long.
  • Required: one time signature at most at a tick.

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The start of the chart

Recommended: a tempo marker and a time signature at tick 0. Edge case: until its first tempo marker, a chart plays at 120 BPM, and until its first time signature, it’s in 4/4.

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Ignored

Tempo anchors. A tempo anchor locks the tempo marker at its tick to a time in the audio, so a chart editor can keep that marker in place while the tempos before it change:
An anchor should share its tick with a tempo marker. Games ignore anchors, and an exporter may keep them.

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Invalid forms

A scanner refuses the file, as Clone Hero and scan-chart do. YARG reads a tempo of 0, which makes its times infinite, and drops the time signatures after a numerator of 0.
A scanner reads a tempo of 2³² or more exactly, as Clone Hero and scan-chart do. It calculates no hash for a file with an exponent of 32 or more, or a numerator of 2³² or more, as scan-chart does, since a BTrack can’t hold such a time signature. Clone Hero reads such an exponent modulo 32, and Clone Hero and YARG read such a numerator modulo 2³². YARG reads a tempo of 2³² or more modulo 2³².
See Syntax: scanners use the later one, and scan-chart’s saving removes the earlier one.