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export function bpmToEighthNoteDuration(bpm: number): number {
// Convert BPM to eighth-note duration in milliseconds
const quarterNoteDuration = (60 / bpm) * 1000; // in ms
const eighthNoteDuration = quarterNoteDuration / 2;
return eighthNoteDuration;
}
function parseTimestamp(timestamp: string): number {
// Parse [mm:ss.ms] format into milliseconds
const [min, sec] = timestamp.split(':');
const minutes = parseInt(min, 10);
const seconds = parseFloat(sec);
return minutes * 60 * 1000 + seconds * 1000;
}
function formatTimestamp(ms: number): string {
// Format milliseconds back into [mm:ss.ms]
const minutes = Math.floor(ms / 60000);
ms %= 60000;
const seconds = (ms / 1000).toFixed(2);
return `${String(minutes).padStart(2, '0')}:${seconds}`;
}
export function adjustTimestampToEighthNote(
timestampMs: number,
eighthNoteDuration: number,
): number {
// Find the closest multiple of the eighth-note duration
return Math.round(timestampMs / eighthNoteDuration) * eighthNoteDuration;
}
function adjustTimestamps(bpm: number, timestamps: string[]): string[] {
const eighthNoteDuration = bpmToEighthNoteDuration(bpm);
return timestamps.map(timestamp => {
const timestampMs = parseTimestamp(timestamp);
const adjustedMs = adjustTimestampToEighthNote(timestampMs, eighthNoteDuration);
return formatTimestamp(adjustedMs);
});
}
// Parse a .lrc file into an array of objects with timestamp and text
// Then adjust the timestamps to the closest eighth note
// Finally, format the adjusted timestamps back into [mm:ss.ms] format and put them back into the lrc object
//
// Example .lrc file:
// [01:15.66] And the reviewers bewail
// [01:18.18] There'll be no encore
// [01:21.65] 'Cause you're not begging for more
// [01:25.00]
// [01:34.64] She may seem self-righteous and holier-than-thou
// [01:39.77] She may sound like she has all the answers
// [01:45.20] But beyond she may feel just a bit anyhow
function parseLrc(lrc: string): { timestamp: string; text: string }[] {
return lrc
.trimEnd()
.split('\n')
.map(line => {
const match = line.match(/\[(\d+:\d+\.\d+)\](.*)/);
const [, timestamp, text] = match!;
return { timestamp, text };
});
}
function formatLrc(lrc: { timestamp: string; text: string }[]): string {
return lrc.map(({ timestamp, text }) => `[${timestamp}] ${text}`).join('\n');
}
function adjustLrc(lrc: string, bpm: number): string {
const lrcArray = parseLrc(lrc);
const timestamps = lrcArray.map(({ timestamp }) => timestamp);
const adjustedTimestamps = adjustTimestamps(bpm, timestamps);
lrcArray.forEach((line, i) => {
line.timestamp = adjustedTimestamps[i];
});
return formatLrc(lrcArray);
}
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