Skip to content

fix(player): keep sync point times exact to avoid drift on non-integer tempos #2960

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
Danielku15 merged 2 commits into from
Oct 17, 2026
Merged

fix(player): keep sync point times exact to avoid drift on non-integer tempos #2960

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
0c276ea
fix(player): keep sync point times exact to avoid drift on non-intege…
Danielku15 Oct 16, 2026
83fb864
test: build repeated alphaTex bars with a loop for Kotlin compatibility
Danielku15 Oct 17, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion packages/alphatab/src/exporter/GpifWriter.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -664,7 +664,7 @@ export class GpifWriter {
}

if (beat.showTimer) {
beatNode.addElement('Timer').innerText = (beat.timer ?? 0).toString();
beatNode.addElement('Timer').innerText = Math.round(beat.timer ?? 0).toString();
}

this._writeBeatProperties(beatNode, beat);
Expand Down
2 changes: 1 addition & 1 deletion packages/alphatab/src/importer/alphaTex/AlphaTex1LanguageDefinitions.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -472,7 +472,7 @@ export class AlphaTex1LanguageDefinitions {
[
[[106], 0],
[[106], 0],
[[106], 0],
[[106], 2],
[[106], 3]
]
]
Expand Down
2 changes: 1 addition & 1 deletion packages/alphatab/src/midi/MidiUtils.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ export class MidiUtils {
* @returns The converted duration in milliseconds.
*/
public static ticksToMillis(ticks: number, tempo: number): number {
return (ticks * (60000.0 / (tempo * MidiUtils.QuarterTime))) | 0;
return (ticks * 60000.0) / (tempo * MidiUtils.QuarterTime);
}

/**
Expand Down
Binary file modified packages/alphatab/test-data/audio/export-sync-points.pcm
View file
Open in desktop
Binary file not shown.
26 changes: 26 additions & 0 deletions packages/alphatab/test/audio/MidiFileGenerator.test.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1933,6 +1933,32 @@ describe('MidiFileGeneratorTest', () => {
expect(actualTimers.join(',')).toBe(expectedTimers.join(','));
});

/**
* See #2952
*/
it('beat-timer-non-integer-bar-duration', () => {
// a 4/4 bar at 148 BPM lasts 1621.6216...ms
const barCount = 200;
const barTex: string[] = [];
for (let i = 0; i < barCount; i++) {
barTex.push('C4.4 { timer } C4.4 * 3');
}
const score: Score = parseTex(`
\\tempo 148
.
${barTex.join(' | ')}
`);

const handler: FlatMidiEventGenerator = new FlatMidiEventGenerator();
const generator: MidiFileGenerator = new MidiFileGenerator(score, null, handler);
generator.generate();

const bars = score.tracks[0].staves[0].bars;
for (let i = 0; i < barCount; i++) {
expect(bars[i].voices[0].beats[0].timer, `bar ${i}`).toBeCloseTo((i * 4 * 60000) / 148, 6);
}
});

describe('metronome', () => {
function testMetronome(tex: string, expectedClicks: string) {
const score: Score = parseTex(tex);
Expand Down
85 changes: 85 additions & 0 deletions packages/alphatab/test/audio/SyncPoint.test.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,13 +6,15 @@ import type { AlphaTabMetronomeEvent } from '@coderline/alphatab/midi/MidiEvent'
import { MidiFile } from '@coderline/alphatab/midi/MidiFile';
import { MidiFileGenerator } from '@coderline/alphatab/midi/MidiFileGenerator';
import type { BackingTrack } from '@coderline/alphatab/model/BackingTrack';
import type { Score } from '@coderline/alphatab/model/Score';
import { Settings } from '@coderline/alphatab/Settings';
import { BackingTrackPlayer, type IBackingTrackSynthOutput } from '@coderline/alphatab/synth/BackingTrackPlayer';
import {
ExternalMediaPlayer,
type IExternalMediaHandler,
type IExternalMediaSynthOutput
} from '@coderline/alphatab/synth/ExternalMediaPlayer';
import type { IAlphaSynth } from '@coderline/alphatab/synth/IAlphaSynth';
import type { IAudioSampleSynthesizer } from '@coderline/alphatab/synth/IAudioSampleSynthesizer';
import type { ISynthOutputDevice } from '@coderline/alphatab/synth/ISynthOutput';
import { MidiFileSequencer } from '@coderline/alphatab/synth/MidiFileSequencer';
Expand Down Expand Up @@ -357,6 +359,89 @@ describe('SyncPointTests', () => {
expect(events.map(e => `${e.currentTime},${e.originalTempo},${e.modifiedTempo}`)).toMatchSnapshot();
expect(testOutput.seekTimes).toMatchSnapshot();
});

/**
* See #2952
*/
describe('non-integer-bar-duration', () => {
// a 4/4 bar at 148 BPM lasts 1621.6216...ms
const tempo = 148;
const barCount = 201;
const ticksPerBar = 3840;
const barMillis = (4 * 60000) / tempo;
const lastSyncTime = (barCount - 1) * barMillis;

function createScore(): Score {
const barTex: string[] = [];
for (let i = 0; i < barCount; i++) {
barTex.push('C4.4 * 4');
}
return ScoreLoader.loadAlphaTex(`
\\tempo ${tempo}
.
${barTex.join(' | ')}
.
\\sync 0 0 0
\\sync ${barCount - 1} 0 ${lastSyncTime}
`);
}

function createGenerator(score: Score, midi: MidiFile): MidiFileGenerator {
const generator = new MidiFileGenerator(score, new Settings(), new AlphaSynthMidiFileHandler(midi));
generator.generate();
return generator;
}

function expectPlayerInSync(player: IAlphaSynth, seek: (time: number) => void) {
const score = createScore();
const midi = new MidiFile();
const generator = createGenerator(score, midi);

player.loadMidiFile(midi);
player.loadBackingTrack(score);
player.updateSyncPoints(generator.syncPoints);

let tick = -1;
player.positionChanged.on(e => {
tick = e.currentTick;
});
player.play();

for (let bar = 0; bar < barCount; bar++) {
seek(bar * barMillis);
const expectedTick = bar * ticksPerBar;
expect(Math.abs(tick - expectedTick), `bar ${bar}: tick ${tick}`).toBeLessThanOrEqual(1);
}
}

it('sync-point-times', () => {
const generator = createGenerator(createScore(), new MidiFile());

const syncPoints = generator.syncPoints;
expect(syncPoints[1].synthTick).toBe((barCount - 1) * ticksPerBar);
expect(syncPoints[1].syncTime).toBe(lastSyncTime);
expect(syncPoints[1].synthTime).toBeCloseTo(lastSyncTime, 6);
expect(syncPoints[0].syncBpm).toBeCloseTo(tempo, 6);
});

it('external-media-position', () => {
const player = new ExternalMediaPlayer(500);
const output = player.output as IExternalMediaSynthOutput;
const mediaHandler = new TestExternalMediaHandler(output);
mediaHandler.backingTrackDuration = lastSyncTime + barMillis;
output.handler = mediaHandler;

expectPlayerInSync(player, time => mediaHandler.simulateSeek(time));
});

it('backing-track-position', () => {
const output = new TestBackingTrackOutput();
output.backingTrackDuration = lastSyncTime + barMillis;
const player = new BackingTrackPlayer(output, 500);

expectPlayerInSync(player, time => output.simulateSeek(time));
});
});
});

describe('MidiFileSequencerCountInTests', () => {
Expand Down
122 changes: 61 additions & 61 deletions packages/alphatab/test/audio/__snapshots__/SyncPoint.test.ts.snap
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ exports[`SyncPointTests > modified-tempo-lookup 1`] = `
"22010.34013605442 => 120.04899959166994",
"24009.52380952381 => 120.04899959167003",
"30007.074829931975 => 80.01088583480758",
"33006.666666666664 => 80.01778172927317",
"33006.666666666664 => 80.01088583480758",
]
`;

Expand Down Expand Up @@ -50,15 +50,15 @@ exports[`SyncPointTests > playback-fast-backing-track 1`] = `
"18496.530140155122,80,160.02177166961516",
"18996.59817662267,80,160.02177166961516",
"19496.66621309022,80,160.02177166961516",
"19996.77706156924,80,160.03556345854633",
"20496.888197377197,80,160.03556345854633",
"20996.999333185155,80,160.03556345854633",
"21497.11046899311,80,160.03556345854633",
"21997.221604801067,80,160.03556345854633",
"22497.332740609025,80,160.03556345854633",
"22997.443876416983,80,160.03556345854633",
"23497.55501222494,80,160.03556345854633",
"23997.6661480329,80,160.03556345854633",
"19996.734249557765,80,160.02177166961516",
"20496.80228602531,80,160.02177166961516",
"20996.87032249286,80,160.02177166961516",
"21496.938358960408,80,160.02177166961516",
"21997.006395427954,80,160.02177166961516",
"22497.0744318955,80,160.02177166961516",
"22997.14246836305,80,160.02177166961516",
"23497.210504830597,80,160.02177166961516",
"23997.278541298143,80,160.02177166961516",
]
`;

Expand Down Expand Up @@ -98,15 +98,15 @@ exports[`SyncPointTests > playback-fast-external-media 1`] = `
"18496.530140155122,80,160.02177166961516",
"18996.59817662267,80,160.02177166961516",
"19496.66621309022,80,160.02177166961516",
"19996.77706156924,80,160.03556345854633",
"20496.888197377197,80,160.03556345854633",
"20996.999333185155,80,160.03556345854633",
"21497.11046899311,80,160.03556345854633",
"21997.221604801067,80,160.03556345854633",
"22497.332740609025,80,160.03556345854633",
"22997.443876416983,80,160.03556345854633",
"23497.55501222494,80,160.03556345854633",
"23997.6661480329,80,160.03556345854633",
"19996.734249557765,80,160.02177166961516",
"20496.80228602531,80,160.02177166961516",
"20996.87032249286,80,160.02177166961516",
"21496.938358960408,80,160.02177166961516",
"21997.006395427954,80,160.02177166961516",
"22497.0744318955,80,160.02177166961516",
"22997.14246836305,80,160.02177166961516",
"23497.210504830597,80,160.02177166961516",
"23997.278541298143,80,160.02177166961516",
]
`;

Expand Down Expand Up @@ -179,24 +179,24 @@ exports[`SyncPointTests > playback-normal-backing-track 1`] = `
"37993.19635324534,80,80.01088583480758",
"38493.26438971289,80,80.01088583480758",
"38993.33242618044,80,80.01088583480758",
"39493.44298733052,80,80.01778172927317",
"39993.55412313848,80,80.01778172927317",
"40493.665258946436,80,80.01778172927317",
"40993.77639475439,80,80.01778172927317",
"41493.88753056235,80,80.01778172927317",
"41993.99866637031,80,80.01778172927317",
"42494.10980217827,80,80.01778172927317",
"42994.22093798622,80,80.01778172927317",
"43494.332073794176,80,80.01778172927317",
"43994.443209602134,80,80.01778172927317",
"44494.55434541009,80,80.01778172927317",
"44994.66548121805,80,80.01778172927317",
"45494.77661702601,80,80.01778172927317",
"45994.887752833965,80,80.01778172927317",
"46494.99888864192,80,80.01778172927317",
"46995.11002444988,80,80.01778172927317",
"47495.22116025784,80,80.01778172927317",
"47995.3322960658,80,80.01778172927317",
"39493.40046264798,80,80.01088583480758",
"39993.46849911553,80,80.01088583480758",
"40493.53653558308,80,80.01088583480758",
"40993.60457205062,80,80.01088583480758",
"41493.67260851817,80,80.01088583480758",
"41993.74064498572,80,80.01088583480758",
"42493.808681453265,80,80.01088583480758",
"42993.876717920815,80,80.01088583480758",
"43493.94475438836,80,80.01088583480758",
"43994.01279085591,80,80.01088583480758",
"44494.08082732346,80,80.01088583480758",
"44994.148863791,80,80.01088583480758",
"45494.21690025855,80,80.01088583480758",
"45994.2849367261,80,80.01088583480758",
"46494.35297319364,80,80.01088583480758",
"46994.42100966119,80,80.01088583480758",
"47494.48904612874,80,80.01088583480758",
"47994.557082596286,80,80.01088583480758",
]
`;

Expand Down Expand Up @@ -269,24 +269,24 @@ exports[`SyncPointTests > playback-normal-external-media 1`] = `
"37993.19635324534,80,80.01088583480758",
"38493.26438971289,80,80.01088583480758",
"38993.33242618044,80,80.01088583480758",
"39493.44298733052,80,80.01778172927317",
"39993.55412313848,80,80.01778172927317",
"40493.665258946436,80,80.01778172927317",
"40993.77639475439,80,80.01778172927317",
"41493.88753056235,80,80.01778172927317",
"41993.99866637031,80,80.01778172927317",
"42494.10980217827,80,80.01778172927317",
"42994.22093798622,80,80.01778172927317",
"43494.332073794176,80,80.01778172927317",
"43994.443209602134,80,80.01778172927317",
"44494.55434541009,80,80.01778172927317",
"44994.66548121805,80,80.01778172927317",
"45494.77661702601,80,80.01778172927317",
"45994.887752833965,80,80.01778172927317",
"46494.99888864192,80,80.01778172927317",
"46995.11002444988,80,80.01778172927317",
"47495.22116025784,80,80.01778172927317",
"47995.3322960658,80,80.01778172927317",
"39493.40046264798,80,80.01088583480758",
"39993.46849911553,80,80.01088583480758",
"40493.53653558308,80,80.01088583480758",
"40993.60457205062,80,80.01088583480758",
"41493.67260851817,80,80.01088583480758",
"41993.74064498572,80,80.01088583480758",
"42493.808681453265,80,80.01088583480758",
"42993.876717920815,80,80.01088583480758",
"43493.94475438836,80,80.01088583480758",
"43994.01279085591,80,80.01088583480758",
"44494.08082732346,80,80.01088583480758",
"44994.148863791,80,80.01088583480758",
"45494.21690025855,80,80.01088583480758",
"45994.2849367261,80,80.01088583480758",
"46494.35297319364,80,80.01088583480758",
"46994.42100966119,80,80.01088583480758",
"47494.48904612874,80,80.01088583480758",
"47994.557082596286,80,80.01088583480758",
]
`;

Expand All @@ -311,7 +311,7 @@ exports[`SyncPointTests > seek-fast-backing-track 2`] = `
4000,
8001.292517006803,
23343.12925170068,
36006,
36006.258503401354,
]
`;

Expand All @@ -336,7 +336,7 @@ exports[`SyncPointTests > seek-fast-external-media 2`] = `
4000,
8001.292517006803,
23343.12925170068,
36006,
36006.258503401354,
]
`;

Expand Down Expand Up @@ -398,8 +398,8 @@ exports[`SyncPointTests > sync-point-generation 1`] = `
"8,0,80,120.04899959166994,24000,22010.34013605442",
"9,0,80,120.04899959167003,27000,24009.52380952381",
"8,1,80,80.01088583480758,36000,30007.074829931975",
"9,1,80,80.01778172927317,39000,33006.666666666664",
"11,0,80,80.01088583480758,48000,42004.666666666664",
"9,1,80,80.01088583480758,39000,33006.666666666664",
"11,0,80,80.01088583480758,48000,42005.44217687073",
]
`;

Expand All @@ -422,7 +422,7 @@ exports[`SyncPointTests > sync-point-update 1`] = `
"8,0,80,120.04899959166994,24000,22010.34013605442",
"9,0,80,120.04899959167003,27000,24009.52380952381",
"8,1,80,80.01088583480758,36000,30007.074829931975",
"9,1,80,80.01778172927317,39000,33006.666666666664",
"11,0,80,80.01088583480758,48000,42004.666666666664",
"9,1,80,80.01088583480758,39000,33006.666666666664",
"11,0,80,80.01088583480758,48000,42005.44217687073",
]
`;
14 changes: 14 additions & 0 deletions packages/alphatab/test/exporter/Gp7Exporter.test.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -184,6 +184,20 @@ describe('Gp7ExporterTest', () => {
expect(gpif).toContain('<MultiVoice>1></MultiVoice>');
});

it('beat-timer-as-integer', () => {
const score = ScoreLoader.loadAlphaTex(`
C4.4 { timer } C4.4 { timer }
`);
const beats = score.tracks[0].staves[0].bars[0].voices[0].beats;
beats[0].timer = 1621.4;
beats[1].timer = 3243.6;

const gpif = readExportedGpif(exportGp7(score));

expect(gpif).toContain('<Timer>1621</Timer>');
expect(gpif).toContain('<Timer>3244</Timer>');
});

it('alphatex-drums-to-gp7', () => {
const tex = `\\track "Drums" { instrument percussion }
\\clef neutral
Expand Down
Loading
Loading