Frame rate & runtime
What a conversion does to runtime, pitch, and motion.
A 90-minute film is 86 minutes 24 seconds on PAL television, and about 90 minutes and 5 seconds on NTSC. This tool converts runtimes between rates and keeps the two families of conversion honest: retimes change runtime and pitch; pulldown and interpolation change structure but keep the clock.
Runtime converter
Duration at one rate, shown at another, with the honest distinction between a retime and a restructure.
Runtime −4% (or +4.17% back). Film-rate material played 25/24 faster for 25 fps television: exactly +4.1667% speed, audio up ~0.71 of a semitone unless pitch-corrected.
2:3 pulldown frame count
Every 4 film frames become 5 video frames.
→ 162,000 video frames at 29.97/30
That’s 1h 30m 0s of film → the same runtime of video (the pulldown adds fields, not time). Cadence: 2:3:2:3 fields. Frame A on 2 fields, frame B on 3, and so on.
Conversion cheat-sheet
| Conversion | Method | Runtime | Watch for |
|---|---|---|---|
| 24 → 25 | PAL speed-up (25/24) | −4.0% (90:00 → 86:24) | Audio +4.1667% speed, +0.71 st: pitch-correct or accept |
| 25 → 24 | Slow-down (24/25) | +4.17% | Asymmetric with the forward trip: +4.17% back vs −4.0% out |
| 24 → 29.97 | Slow to 23.976, then 2:3 pulldown | +0.1% | Pulldown judder; edits after pulldown break the cadence |
| 24 ↔ 23.976 | 1000/1001 retime | ±0.1% | Inaudible pitch, but sync drifts 3.6 s/hour if one side forgets |
| 25 → 50 | Frame doubling | Unchanged | Clean; no new motion information |
| 25 ↔ 29.97 | Standards conversion (interpolation) | Unchanged | Quality lives or dies on the converter; artefacts on fast motion |
PAL speed-up, precisely
Film-rate material is broadcast at 25 fps by playing it 25/24 faster: exactly +4.1667%, not the “4%” of folklore. Runtime shrinks by the reciprocal (−4.0%), and unconverted audio rises by 12 × log₂(25/24) ≈ 0.71 of a semitone, audible on sustained music, which is why modern workflows pitch-correct.
Pulldown, briefly
NTSC-land takes the other path: 24 is first slowed by 1000/1001 to 23.976 (+0.1% runtime), then every four film frames are spread across five video frames as 2:3:2:3 fields. Nothing is retimed beyond that 0.1%, so runtime is essentially preserved. The cost is motion cadence (pulldown judder) and fragility: cut the video after pulldown and the cadence breaks, which is what makes clean reverse pulldown hard.
SpectraQC verifies frame rate, scan type, and cadence against your delivery spec: see the video checks.