Doubts about possible tempo issues

[sandrojologua]

Hello there, I think there are some issues regarding tempos in alphaTab. For example, if you look at this guitar pro file - https://tabs.ultimate-guitar.com/tab/iron-maiden/fear-of-the-dark-guitar-pro-222083 - And import it in alphaTab, then you will see that tempos are incorrect, for example in 24th measure the tempo is really low. This doesn't happen when running the same file in Guitar Pro 8. Actually, I think this is a problem from parsing the file, it doesn't correctly retrieve all the tempo changes inside the file.

Thanks 🙏

[Danielku15]

Your assumption is partly true. alphaTab reads all tempo changes correctly into the data model but currently does not show and handle multiple tempo changes within a single bar/measure correctly. Your example file makes heavy use of this.

I added #1207 as dedicated work item to handle this in future. But I cannot commit to any date to ship this extension yet. But maybe i can provide at least an improvement that the last tempo change wins then at least the tempo might only be a bit messy within the affected bars but then the song continues correctly

[sandrojologua]

@Danielku15 Thanks for the response.

I can't see that data model has all tempo changes correctly, although I trust you to know this library better than me.

Please take a look at this code snippet. My eventual goal is to compute timestamps for each note. But before that I want to detect all tempo changes correctly. One example would be that it doesn't detect tempo change to 210 bpm in measure 24.

const alphaTab = require('@coderline/alphatab');
const fs = require('fs');

data = [];

function parseGpFile(filePath) {
    const score = alphaTab.importer.ScoreLoader.loadScoreFromBytes(
        new Uint8Array(fs.readFileSync(filePath)),
        new alphaTab.Settings()
    );

    // Extract tempo and initialize current time
    let tempo = score.tempo;
    let currentTime = 0;

    for (const staff of score.tracks[1].staves) {
        for (const bar of staff.bars) {
            if (bar.masterBar.tempoAutomation && bar.masterBar.tempoAutomation.type === 0) {
                tempo = bar.masterBar.tempoAutomation.value;
                console.log(`tempo change to ${tempo} in bar ${bar.index + 1}`)
            }

            // console.log(`#${bar.index + 1} ${bar.masterBar.timeSignatureNumerator}/${bar.masterBar.timeSignatureDenominator} ${tempo}`);
            let partHere = 0;
            for (const voice of bar.voices) {
                // Iterate over beats in each voice
                for (const beat of voice.beats) {
                    const measureDuration = (60 / tempo) * bar.masterBar.timeSignatureNumerator;

                    for (const automation of beat.automations) {
                        if (automation.type === 0) {
                            tempo = automation.value;
                            console.log(`tempo change to ${tempo} in bar ${bar.index + 1} and beat ${beat.index}`)
                        }
                    }

                    let part = 1 / beat.duration;
                    // Check for dotted duration and tuplet
                    if (beat.dots > 0) {
                        part += part / 2;
                    }
                    if (beat.tupletNumerator !== beat.tupletDenominator) {
                        part *= beat.tupletDenominator / beat.tupletNumerator;
                    }

                    partHere += part;
                    if (partHere > 1) {
                        break;
                    }

                    let chord = [];

                    // Log each note in the beat
                    for (const note of beat.notes) {
                        chord.push({
                            'string': note.string,
                            'fret': note.fret,
                            'timestamp': currentTime
                        });
                    }

                    data.push(chord);

                    currentTime += measureDuration * part;
                }
            }
        }

    }
}

// Replace with the path to your Guitar Pro file
parseGpFile('Iron Maiden - Fear Of The Dark.gp4');