Hacker News Reader

Comment by discreditable | Hacker News Reader

One problem is that TVs run at 60fps and don't support adaptive sync. 60 is not evenly divisible by 24. Without some kind of trick you're padding to 30fps by duplicating every 4th frame, or trimming to 20fps by dropping every 6th frame.

Padding is usually what's done. You can see it in NTSC (30fps) DVDs which come from something originally produced for PAL (25fps). Every 5th frame is duplicated.

It makes me curious what framerate movie projectors run at. Maybe the "cinema experience" includes goofy frame duplication and nobody realizes it.

View on HN

Traditionally, each film frame is projected 3 times. The psycho-perceptual reason is that the phi-phenomenon (“light chaser effect”) kicks in about 12–15 Hz, so camera frame rate must exceed that to give a perception of smooth motion. The critical flicker frequency is around 50 Hz for most people, so projected frame rate must exceed that to avoid the appearance of flickering.

Silent movies were shot 18 fps and projected 54 fps. The frame rate for talkies was boosted to allow enough bandwidth for the audio. The reason silent movies look jerky today is every third frame is projected twice. They are smooth when properly projected.

50Hz is below the flicker fusion threshold for most people. Even 60Hz visibly flickers for many people.

Silent movies were shot and projected at many different framerates. Some early silent movies were shot at 18fps, but the average frame rate increased over time, and the standard 24fps was picked as a compromise that was around the average frame rate at which films were displayed at that time.

Nowadays with digital TVs that conversion between frame rates is completely pointless. The playback device just switches to a different frame rate and resolution and the tv should adapt. My cheap TCL TV accepts different rates just fine. I can somewhat understand that they keep doing that for DVD releases since someone somewhere might watch it on their old trusty CRT, but other than that you might as well just import the release that has the original frame rate. Oh wait, there are those region codes right? opens the pirate bay ...

https://en.wikipedia.org/wiki/Three-two_pull_down

Reply on news.ycombinator.com