Linear speed increase impossible in Davinci Resolve?

Let's say I have a clip that is 5 seconds long. Now, I want the clip to begin with a speed of 50%, and end with a speed of 100%, and I want the speed to gradually increase until it reaches 100%.

I haven't found any way to do such a linear speed increase in Davinci Resolve. I couldn't believe it at first, because even my amateur video editing programs that I used years ago could do that. So please correct me if I'm wrong. But I double checked, and watched many tutorials on Speed Ramping in DaVinci Resolve, but none of them say anything about how to create a gradual, linear increase in speed in Davinci Resolve.

Is linear speed increase and decrease impossible in Davinci Resolve?

It depends what you want exactly. If you specifically want a linear speed increase, then no, I'm not sure if that's possible.

If you want a smooth change in speed from speed X to speed Y, then that is possible:

If you show the Retime Speed keyframes, and set them to curved, you can achieve this:



In this example, this does a smooth change in speed from 10% to 100%. You could equally do 50% to 100%, or vice versa.

I tested it with a clip where it was easy to judge the speed, and the smooth change in speed appeared to work OK.

The keyframe graph indicates the change in speed is a smooth curve, so it's not a strictly linear change. At least, if the graph is accurately representing what's happening (in other examples in Resolve, it claims to be smooth but is actually linear, so I'm not certain in this case.)

There's definitely some deficiency here, as there should be the option to choose between linear and smooth, but the options choose between (apparently) smooth, and instantaneous, like this:



Personally I would think the smooth option is going to be fine for most use cases, but yes it's a shame this keyframe editor lacks all the options it would be expected to have.

So it's impossible to have a linear speed increase or decrease in Davinci Resolve.

So it's impossible to have a linear speed increase or decrease in Davinci Resolve.

Assuming the curved graph is accurately representing a curved change - and it's possible it's not, as elsewhere it fails to do a smooth curve when it claims to - then yes, on the Edit page you can't do a linear speed change.

You should however be able to do this in Fusion, using the TimeStretcher node, which allows keyframing the current frame and then using the fantastic Spline Editor to do any kind of speed changes you want - linear, any kind of smooth curve, etc. There's also the community-made TimeMachine node which offers even more options.

To do it in Fusion, you could place an Adjustment Clip above one or more clips. Then manipulate the timing of the MediaIn1 node as desired.

I haven't done it myself, but it should work in theory.

Dang, Bloke beat me again. Came here to say basically the same thing. You can stairstep the speed, and smooth the transition points in-between.

This has been asked before. viewtopic.php?f=21&t=118990&hilit=+spee
I will go a step further and say that linearly increasing something's speed isn't the same thing as constant acceleration. Gravity pulls an object towards the earth at 9.8 meters per second^2. If you drop something from the top of a tall place, it's starting at zero M/s, and going faster and faster until it hits the ground, but it's acceleration is always 9.8 M/s^2.

Here are two graphs from Cinema4D, where you *can* see both position as a function of time (yellow) and speed as a function of time (red). The first example shows constant speed, which is the same as zero acceleration. The animated box moves left to right in what animators would say is a "linear" motion, with no "ramping."

Screen Shot 2020-09-10 at 0314 1.png (52.93 KiB) Viewed 12705 times

In the second example, I tried to manipulate the bezier position handle to make the red velocity curve form a line with a constant slope. It's not easy, as the velocity curve bends in "S" shapes in ways you wouldn't expect, and if you look closely, you'll notice at the beginning, there is some curve, and it actually dips below zero at the very beginning.

Screen Shot 2020-09-10 at 0318.png (58.93 KiB) Viewed 12705 times

But what happens to the position curve when I do this, is that it starts to look more like a logarithmic curve (at least, the Log curves us liberal arts majors are used to seeing; not sure if that's mathematically accurate). And in this example, the box animates in a fashion that animators would recognize as "ease out."

Moral of the story: If you're really trying to linearly accelerate something, look no further than "ease out," which Resolve does just fine.

Constant acceleration curve is essentially parabolic shape in position curve if starting from 0 velocity. There is an easy method for approximating it by placing the curve handles at specific coordinates relative to keyframe positions but I can’t remember it at the moment...

Moral of the story: If you're really trying to linearly accelerate something, look no further than "ease out," which Resolve does just fine.

So are you saying that the smooth curve shown on the Edit page Retime Speed is a linear speed adjustment? Retime Speed doesn't seem to offer 'ease in' and 'ease out' as such, it just gives you two horizontal handles which can be made wider or shorter, with both adjusting at the same time.

In other words, it appears to my eyes to be simultaneously applying ease-in and ease-out of varying amounts. And because the line is curved, it makes it seem like the speed adjustment is also curved, not linear?

But you're saying this is actually a linear increase in speed?

Personally I can't imagine it would even be that easy to tell the difference in a real clip, but the OP seems to want linear specifically.

To do it in Fusion, you could place an Adjustment Clip above one or more clips. Then manipulate the timing of the MediaIn1 node as desired.

Actually it seems it's not possible to do this in a Fusion Adjustment Clip.

I don't think Adjustment Clip Fusion compositions work with time adjustments. All my attempts using TimeStretcher or TimeMachine nodes give very strange results, where sometimes the time adjustment works, and sometimes it does the opposite of what I wanted. Eg trying to run a clip at 10% speed, on frame 144 it might correctly show frame 14, then on frame 145 it shows frame 158!?

EDIT: I think I found a workaround, by putting the clip in question in a Fusion Clip, artificially increasing the length of the Fusion Clip by putting some random clip on Layer 2, then putting a Fusion comp on the Fusion Clip, using a TimeStretcher node to retime MediaIn1.

The TimeStretcher node now works fine for retiming MediaIn1, with none of the weird glitches I saw with an Adjustment Clip.

The workaround of putting random stuff on layer 2 is necessary so the Fusion Clip's length can be increased beyond the length of the original clip, which will be necessary if any reduction in the clip's speed is required. You can't extend a Fusion Clip (or any timeline-like clip) to be longer than its contained media, hence putting extra stuff on layer 2 so its length can be increased. A Fusion Clip will see the video layers via separate MediaIn nodes, so extra stuff on layer 2 will be in MediaIn2, and won't affect MediaIn1.

Constant acceleration curve is essentially parabolic shape in position curve if starting from 0 velocity. There is an easy method for approximating it by placing the curve handles at specific coordinates relative to keyframe positions but I can’t remember it at the moment...

Yeah, parabolic! That's the word I was looking for! Makes sense, too, right? Because if you think of a ballistic path, like a baseball or cannonball, it makes a parabola.

Here's a video showing the difference between constant speed and constant acceleration. The slope of the dark red line (the one without bezier handles) is acceleration, so when the red line is bendy, it's not constant. When it's straight horizontal, it's zero acceleration, which is the same thing as saying constant speed. When it has a positive, straight slope, there's constant acceleration, which is the same way gravity works. I'm not sure if any of Resolve's easing methods (there's a variety on the color page, but only one kind on the edit page) are exactly linear acceleration, but I don't think it matters as much to editors and colorists as it does to engineers, and they're using MatLab or something else, anyway.

Sorry the video's so bad. This is why I don't do youtorials.

That's very interesting, Jason. I wish Fusion could show velocity like that.

I've been doing some experimenting. I used a community-made Fuse called Retimer.

This is a really nice tool. It allows simple keyframing of Speed, and interprets that in the way you'd intuitively expect. From the description:
Retimer lets you retime your footage or 3D scene but it calculates the retiming on a frame basis.
This means that if you're on frame 100 and changes the speed from 1 to 2, the next frame will be 102 while if you would simply change the clips speed you would end up at frame 200.

(Unfortunately Retimer currently doesn't work in Resolve's Fusion page - it needs a one line fix to make it work, which I've made the author aware of and will be pushed to Reactor hopefully tomorrow. In the meantime, the Time Machine fuse can be used in Delta mode, keyframing Delta with the same keyframes shown for Speed below:)

Using Retimer, I set the following keyframes:
> Frame 0 : Speed 0.1
> Frame 450: Speed 0.1
> Frame 900: Speed 1.0

Therefore this gave me:
> Frames 0 - 449 : 10% speed
> Frames 450 - 899 : speed increasing from 10% to 100%
> Frame 900+ : 100% speed

I then added a TimeStretcher node, keyframed it, and manually adjusted the spline handles attempting to achieve the same output as the Retimer. I eventually achieved a near 1:1 match with the following graph (white = TimeStretcher's Source Time; red = Retimer's Speed)


I needed to curve the TimeStretcher Source Time graph in order to replicate a speed increase from 10% to 100%, which in hindsight was obvious: a graph of the current frame number must be curved if the speed is changing over time.

Based on what Jason showed, I think this speed increase would be considered constant acceleration? Speed increases from 10% to 100% over 450 frames, an increase of 0.2% per frame. Given the playback rate is 30 FPS, the rate of acceleration is 0.06 frames-per-second per frame?

I later tried to replicate something like this using the Edit page Retime Speed controls, but couldn't get anywhere near to the same result. It seems to be restricted with regards to the speed changes you can achieve, because you can only pull the handles out so far. It doesn't work like a normal keyframe system, where a curve is defined between two keyframes. On Retime Speed, a curve is defined around a single keyframe. So using Retime Speed I couldn't create anything close to the speed change I defined in Fusion, because the handles wouldn't drag out nearly far enough.

On top of that, I found it nearly impossible to get precise results, because the granularity of keyframe movement is severely lacking. The smallest movement I could make of a Retime Speed keyframe resulted in a 6 frame jump in the clip.

Then I tried with Edit page's Retime Frame. Again I came up against the sensitivity/granularity issue, finding it close to impossible to make precise adjustments in keyframes. So I settled for getting the output within 5 frames of the Fusion result. Having achieved that with the Retime Frame keyframes, I then switched the display to Retime Speed, and it showed this graph:


So it interpreted that speed change as two instantaneous speed changes, dividing the clip into three time ranges: 10% speed at the start, 100% at the end, and 55% in the middle, which is apparently the average speed necessary to increase speed from 10% to 100% at a constant rate.

In my opinion, the TLDR of all this is: Use Fusion for any retiming that needs precise control, or where you want to be able to guarantee the rate of change. At least if it doesn't involve audio, of course.

There's a little extra hassle involved in using Fusion for retiming, because Adjustment Clips don't work and if you want to slow a clip down you need to put it in a Fusion Clip, then artificially increase the length of that Fusion clip.

But it's possible to get much more precise and specific control in Fusion than it is using the Edit page keyframes - especially with the Retimer Fuse, which is nice and simple to use and understand. For even more sophisticated control - albeit a little harder to get your head around - there's also the excellent TimeMachine Fuse, which has 12 separate time manipulation modes, and also works as a Modifier - meaning it can manipulate time not only for images and 3D scenes, but also number and position values on any node.

two horizontal handles which can be made wider or shorter, with both adjusting at the same time.

If you CTRL+Click on one of the handles, it'll move independently of the other, allowing some more flexibility.

two horizontal handles which can be made wider or shorter, with both adjusting at the same time.

If you CTRL+Click on one of the handles, it'll move independently of the other, allowing some more flexibility.

Thanks for the tip.

Thank you guys for an extremely interesting and useful research.

Hopefully, linear speed increase will be possible in DR18. It's so basic. Lots of Amateur programs like MAGIX Video Deluxe can do it for more than 10 years ago. I can't believe Davinci Resolve, a supposedly professional program, can't do it.

I found an option for speed ramp for a clip. It is under the Retime Controls, but is not always visible. I had to convert my modified clip to a compound clip and then it showed up.

Here is where I found it: select clip, turn on Retime Control, click on bottom of clip 100% arrow to pull up menu.

I was able to move some of the sliders around after the speed ramp was in place too, to make additional adjustments, but still figuring it all out.

Linear speed increase and decrease still impossible in Davinci Resolve 18.

Resolve 19 still can't do it

trying to speed up the clip from 25% to 800% linearly

when you try to do something similar to linear speed change with the curved transition, the curved line controls on the right side of the clip jumps out of the clip, so you can't adjust them anymore