Speed Ramp
Also known as: Variable Speed Effect
What Is a Speed Ramp?
A speed ramp changes a clip’s playback speed gradually instead of in one jump, most often from normal speed down to slow motion and up again. The goal in a match, the top of a jump or a product turning toward the camera slows down while the rest of the shot keeps its pace, and no cut breaks it up.
Final Cut Pro builds a ramp from speed segments, parts of a clip that each play at one constant speed, and joins them with speed transitions, and its guide calls the result a variable speed effect. Editors with time remapping draw the same change as a curve with keyframes, which is how the solid line below was made.
How Do You Shape the Speed Change in a Ramp?
Give the change a stretch of its own and a curve that leaves the old speed and arrives at the new one, so there is no single frame where the speed switches. We tested three ways of keyframing a slowdown from 1x to 0.25x on a time curve, by exporting a 30 fps test clip and reading back which source frame each exported frame showed.
Spread the change over its own stretch
With straight keyframes, the clip went from 1x to 0.25x between one frame and the next, which reads as a hard switch. Final Cut Pro does the same between two speed segments until you add a speed transition, and its guide notes that a shorter transition gives a quicker ramp.
Skip ease presets on the time curve
An ease-in-out preset on each keyframe eases the time value itself, so the clip slowed to a stop at every keyframe and sped up in between. In a stretch that averaged about 1.7x, it peaked at 3x, which looks like a stumble rather than a ramp.
Match the curve to the speed on each side
Bezier handles set to leave the keyframe at 1x and arrive at 0.25x gave an even fall over one second, and the same handles in reverse brought the clip back up. That is the solid line in the chart above, and the speed never stopped or overshot.
Why Does Slow Motion Stutter in a Speed Ramp?
Footage shot at the frame rate of the finished video runs out of frames once it slows down, so each frame stays on screen longer unless software draws new ones in between. At 0.25x, a 30 fps clip in our 30 fps CE.SDK export showed each of its frames four times, while a clip shot at 120 fps gave a new frame every time. Final Cut Pro’s guide uses the same 120 fps in a 30 fps project as its example, and its frame blending and optical flow settings build in-between frames from the frames around them.
4x
each 30 fps frame on screen at 0.25x
46 different frames in 180 exported ones
180 of 180
exported frames that were new
when the 0.25x clip was shot at 120 fps
120 fps
to shoot for 0.25x in a 30 fps video
the export frame rate divided by the speed
When Should You Use a Speed Ramp?
Use a speed ramp when one moment inside a continuous shot deserves a closer look, such as a skateboard trick that slows to 0.25x at the top of the jump and speeds back up for the landing. When a whole clip only needs to run shorter or longer, one constant speed does the job.
| Use | Why | |
|---|---|---|
| A goal, a jump or a trick in a sports clip | A ramp into 0.25x just before the moment and back out after it | The play keeps its pace, and only the moment that matters slows down |
| A product reveal in an ad | A ramp down to a hold on the product | The motion slows to a stop, so the product sits still on screen before the cut |
| An edit cut to a song | Ramps timed to the beats | The slow and fast parts land on the music instead of between beats |
| A long process, such as a recipe or a build | One constant speed between 2x and 4x, no ramp | No single moment needs a closer look, and a steady pace is easier to follow |
| Someone talking to the camera | Speech at 1x, with ramps on the b-roll only | Even with the pitch kept, words at another speed are harder to follow |
| Footage shot at 30 fps that has to slow to 0.25x | A short slow part, or 0.5x instead | At 0.25x each frame shows four times, which reads as stutter over a long stretch |
How Clip Speed Works in CE.SDK
In CE.SDK video editing, your users set the speed of each clip in the editor, and your code can change it as well, including on a server for videos your backend renders.
Users set a speed for each clip
Selecting a video clip shows a speed control in the inspector bar, with presets from 0.25x to 10x and a field for any value in that range, and audio clips go from 0.25x to 3x. The clip gets longer or shorter to match, so a 6 second clip set to 0.25x fills 24 seconds of the timeline. On iOS and Android, the editor has a speed control too.
Code sets speed, audio keeps pitch
The same setting is open to your code for video, GIF and audio clips, for example to slow every clip in a template to 0.5x. In our export, an audio clip of a 1 kHz tone stayed at 1 kHz at both 0.5x and 2x. Above 3x, the engine mutes a video clip’s own sound until the speed comes back down.
FAQs
No. Slow motion plays a clip slower than real time at one steady speed, while a speed ramp is the gradual change between two speeds, usually on the way into slow motion and out of it. Final Cut Pro keeps them apart as well: a constant speed change for slow motion, and speed segments with transitions between them for a ramp.
Time remapping is the tool, and a speed ramp is one thing you make with it. A time remap decides which moment of the source shows at each point of the output, so it can also freeze a clip, play it backward or play a stretch twice.
Divide the frame rate of the finished video by the slowest speed in the ramp. For 0.25x in a 30 fps video that comes to 120 fps, and for 0.5x it comes to 60 fps, so every exported frame of the slow part gets a source frame of its own.
Not by default in Final Cut Pro, and not in our CE.SDK test. Final Cut Pro keeps the pitch of a retimed clip unless you turn off Preserve Pitch to make the speed change easier to hear. In our CE.SDK export, an audio clip of a 1 kHz tone stayed at 1 kHz at both half and double speed.
Links
Documentation and references for this concept.
Video Editor SDK
Give your users a speed control on every video clip, from 0.25x slow motion up to 10x.
Playback Speed API
Give a video, GIF or audio clip a new speed from your code, and its length on the timeline adjusts to match.
Audio Speed Guide
Change the speed of an audio clip from 0.25x to 3x, in the timeline or from your code.
Related Terms
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