Overview: Timing and synchronization

Subtitle timing places cues on the media timeline and distinguishes offsets, drift and edition-specific mismatches.

If every cue is late by the same amount, the timing problem differs from one that grows as the programme continues. Frame-based timing introduces another relationship, and a differently edited edition may resist a single correction altogether. This branch gives those symptoms distinct names and connects them to the cue and timestamp representation.

• Subtitle cues
  A subtitle cue is a timed presentation item whose active interval and content determine what a renderer presents at a media instant.

• Subtitle timestamps
  Subtitle timestamps express presentation positions whose meaning depends on their syntax, unit, time base and timeline origin.

• Subtitle time offsets
  A subtitle time offset moves all applicable cue boundaries by the same amount without changing the cue durations or spacing.

• Subtitle timing drift
  Subtitle timing drift is a growing synchronization difference caused by a time-scale mismatch or another changing relationship between subtitles and the programme.

• Frame-based subtitle timing
  Frame-based subtitle timing maps numbered frames to presentation time using the correct rate, frame origin and boundary convention.

• Subtitle edition mismatches
  Subtitle edition mismatches arise when subtitles and video refer to different scene sequences, requiring more than one global time adjustment.