Let’s tackle your questions one by one, starting with the handy conversion function you need for audio cross-referencing.

1. Convert SRT Timestamp to Milliseconds #

Here’s a no-fuss JavaScript function built specifically for your SRT timestamp format (HH:MM:SS,mmm):

function srtTimestampToMs(timestamp) {
  // Swap comma to dot to align with JS's time parsing conventions
  const [timeSegment, msSegment] = timestamp.replace(',', '.').split('.');
  const [hours, minutes, seconds] = timeSegment.split(':').map(Number);
  
  // Calculate total milliseconds
  return (hours * 3600 + minutes * 60 + seconds) * 1000 + parseInt(msSegment, 10);
}

// Quick test:
const exampleMs = srtTimestampToMs('00:00:11,544');
console.log(exampleMs); // Output: 11544

This handles the SRT-specific comma separator for milliseconds and breaks down the time units into a single millisecond value—perfect for syncing with audio playback APIs.

2. Is This Timestamp a Standard Format? #

Absolutely! This is the official, standardized timestamp format for SubRip (SRT) subtitle files. The SubRip spec defines timestamps as HH:MM:SS,mmm where:

• HH = 2-digit hours (00-99)
• MM = 2-digit minutes (00-59)
• SS = 2-digit seconds (00-59)
• mmm = 3-digit milliseconds (000-999)
  The comma separating seconds and milliseconds is the key difference from ISO 8601 time formats, which use a dot.

3. Can It Be Easily Converted to a Date Object? #

Not directly—and here’s the context you need:

• SRT timestamps are relative time offsets (counted from the start of the audio/video file), not absolute calendar dates/times. A Date object is designed to represent specific moments in time, so converting an SRT timestamp alone doesn’t have inherent meaning unless you pair it with a known start time of the media.
• If you do need a Date object (e.g., to sync with a media’s broadcast timestamp), you can:
  1. Convert the SRT timestamp to milliseconds using the function above.
  2. Add that offset to the media’s absolute start Date.

For example:

const mediaStartDate = new Date('2024-05-20T14:30:00Z');
const srtOffsetMs = srtTimestampToMs('00:00:11,544');
const syncDate = new Date(mediaStartDate.getTime() + srtOffsetMs);
console.log(syncDate.toISOString()); // Output: 2024-05-20T14:30:11.544Z

If you’re just syncing with media playback, sticking with the millisecond offset is usually simpler than working with Date objects.

内容的提问来源于stack exchange，提问作者Lee Probert