Thiago, o meu amigo, ti tenhes os numeiros un poquinho descalabrados
most film is shot (and projected
) at 24 frames per second. Color NTSC runs at 60 Hz (59.94Hz to be exact
) and PAL runs at 50 Hz (Hz = interlaced fields, or "half frames")
When a 24fps movie is transfered to PAL, to make things easy and pretty, the film is run slighly faster (4%) at 25 frames per second and the frames are divided into the 50 fields (the "half frames", a frame would be composed of 2 interlaced fields)
If they didnt run the film at 25fps they would have to repeat a frame every second (24 becomes 24 +1 repeat = 25) and that would do a very noticeable jerky motion happening once every second, 60 times a minute, 3600 times and hour; nobody could last that long watching movement jerking one time a second
This 24fps -> 25fps results in the movie running (being played back) 4% faster but trhe motion is perfectly smooth and totally fluid cus there are NO frame repeats. Great for action and animation
Some people are more sensitive to sound pitch changes than others and might notice the change in sound readily while others might not.
(I even see the difference in visual speed slightly
)
When a 24 fps film is transfered to NTSC's 60 Hz, it's split into 48 fields and the fields are repeated in a 2:3 cadence which means a field of every second frame is repeated again (or something like that
) (if you wana see an illustrated example search the web, "3:2 pulldown", it's easier to understand watching illustrations than me exaplaining it
) bringing the number of fields from 48 up to 60 to match the NTSC 60 Hz speed.
When watching film DVDs on a progressive 60hz NTSC display, the full 24fps are recuperated and doubled, and then every other frame is repeated one more time bringing the frames up to 60 from the doubled 24.
These repeats/jerkiness then happen 12 times a second, 720 times a minute, 43,200 times an hour so they look smooth enough for most casual viewers to go mostly unoticed but if you look closely you could detect them (i use Leslie Caron twirling around redstripe shirted Gene Kelly in An American In Paris as an example
)
Since the repeats "convert" the 24 fps directly to 60Hz without changing the time space continuum
the film stays 24->24 in speed and runs at normal rate. (Actually it runs at 23.976 fps cus Color NTSC is really 59.94 Hz but i'd think NTSC's 0.1% slowdown would be very hard to detect
except for someone that has ultraperfect pitch
496. After watching Titanic, thinking for 6 minutes how great it woulda looked in
Blu-ray.
