I was a bit surprised to know that some video editors still struggle with finding the optimal approach when it comes to pulling off perfectly smooth and seamless slow-motion videos. Sure, you have to work with media that was shot at 60fps or higher to be able to get some decent results.
Nevertheless, there are still some misconceptions regarding the way one should treat this footage inside Premiere Pro CC. The truth is, you can conform those clips in multiple ways and get some excellent results each and every time. Here are two of the easiest and most straightforward methods you could opt for.
Once you have your video clip inside Premiere Pro CC, throw it on your timeline and by right-clicking on it, choose Speed/Duration. Normally, you’d like to set your speed to 50%, even though when you’re working with a 60fps clip on a 24fps timeline, 30% should be just fine.
Now, here’s the trick. When you are utilizing this particular workflow it’s quite normal to get choppy and uneven results, unless you enable Optical Flow processing under Time Interpolation at the bottom of the Speed/Duration dialog box. Typically, when you select Optical Flow, you’ll need to render out the effect once it’s applied to your clip. You can easily do so, by setting up in and out points at the beginning and the end of your clip as shown in the video above.
After that, go to Sequence in the top menu and choose Render In to Out. This function will render just the edit that is located between the in and out points you’ve previously created on your timeline. Keep in mind, that Optical Flow will add some extra frames in order to emulate the perfect slow motion.
Normally, these additional still images shouldn’t be visible when you play back your clip in real-time, but if you scrub through it frame by frame, you’ll be able to spot them much easier. Optionally, you can take this process one step further by using Time Remapping function and adding keyframes manually so that you can have even greater control over the process.
Another way to achieve the same effect, but with more precise results is by conforming the clips in advance. Unlike the previous method, however, you should select the clip that you want to conform directly in the Media Browser.
Once your clip is selected, right-click on it, go to Modify and choose Interpret Footage. All you have to do in this dialog box is select Assume this frame rate and enter the desired frame rate. For instance, if you have a clip shot at 60fps and your timeline is set to 23.976fps, enter the latter value and hit OK.
Now, when you drag your clip into the Sequence, it will be slowed down while playing back at 23.976fps. As a rule, always conform your footage right after you import it in Premiere Pro CC to save the hustle to re-time your shots after you’ve already made edits.
Either way, you’ll be able to get some perfect slow motion videos while using these two different methods. It may sound obvious, but always make sure that you’re working with clips that are shot at a higher frame rate (60fps at least) to be able to get the smoothest and seamless results possible later in post.