Why do silent films look sped up?

Same frames,
different time.

Momo rides a trolley across a small stage in four seconds. Record its movement, then change how quickly the recorded frames pass. The journey stays the same. The time given to it changes.

Explore the same four-second journey, or read the timing table below. Nothing moves until you choose Play.

Capture rate · recorded frames/sHow many images we record each second.

Projection rate · source frames/sHow many recorded images we advance each second.

Try a pair · capture → projection

Projected movement1.5× speed · faster

Recorded in 4 seconds64 frames

Time to project every frame2⅔ seconds

Original movement

Continuous reference

Original time 0.000 s / 4.000 sThe movement before any frames are recorded.

Projected frames

Recorded images held

Frame 1 of 64 · recorded at 0.000 sProjection time 0.000 s / 2.667 s

Shared elapsed time: 0.000 sReady · no motion until you choose Play

Inspect time

Each step advances the shared clock by 1/24 second. Stepping or scrubbing pauses playback.

Use still frames onlyKeeps frame steps available. Initially follows your device’s motion preference.

Inspect the depth · while pausedView: front · elevation 24°

Both views change together. Reset view restores the fixed-depth front view.

Look at the time, then the steps.

At 16 → 24, one second of playback advances through 24 recorded frames: 1.5 seconds of the original movement. Momo moves ahead in the projected view. In that view, his position changes only when the next recorded frame begins.

A stage with depth. One simple journey.

Momo rides the middle rail at a constant speed, keeping the same pose. The short posts are in front; the taller columns are behind. In the front view, the journey stays at the same camera depth.

You can read the result without playing it

Three images from the same strip

These are selected recorded frames, shown from the fixed front view. Compare when each image was captured with when it first appears in projection.

Frame 1 · startRecorded at 0 s
Projected from 0 s

Frame 17 · a quarter acrossRecorded at 1 s
Projected from ⅔ s

Frame 33 · halfway acrossRecorded at 2 s
Projected from 1⅓ s

The same recorded positions, with capture and projection times
Recorded image	Captured at	Projection begins at
Frame 1	0 s	0 s
Frame 17	1 s	⅔ s
Frame 33	2 s	1⅓ s

4 s × 16 frames/s = 64 frames. 64 frames ÷ 24 frames/s = 8/3 s (2⅔ s). Speed: 24 ÷ 16 = 1.5×.

The last image is recorded at 3.9375 s. It stays on screen for 1/24 s, just like every other frame. The strip therefore lasts 2⅔ s. There is no extra recorded frame at 4 s.

How the frames are counted

For a four-second movement, capture rate c gives 4c frames. Frame k is recorded at k/c and held from k/p to (k+1)/p in projection. No extra frame is recorded at four seconds. A finished view holds its last position while the other finishes.

This invented scene compares timing. It does not recreate a projector’s shutter, exposure or flicker; screen refresh can affect which updates you see. Silent films had no single frame rate.

Controls and still mode

Use Tab, Enter and the arrow keys. Rate changes return to the first frame. The camera moves only while paused. Still mode follows your device preference and keeps frame steps available. Leaving the tab pauses playback; returning does not restart it.

Four seconds, four settings

Capture → project	Frames	Screen time	Speed
16 → 16 fps	64	4 s	1×
16 → 24 fps	64	2⅔ s	1.5×
24 → 16 fps	96	6 s	⅔×
24 → 24 fps	96	4 s	1×

Changing projection speed changes the time given to the recorded images. Their order stays the same.