|Interlacing Progressive Footage|
I've used one of my stock footage clips from my collection at RevoStock.com called, "Brady Bunch Tiki: V2" as a test clip to use as an example for this article. This original clip is 1080p24 (and is also supplied as 720p24, 576p25 PAL and 486p24 NTSC at RevoStock). For this tutorial, I created a master file by conforming it from 24p to 30p and reduced it down to SD letterbox 4x3. It's from this converted SD file on which we'll perform all our tests. I thought this clip would work well for this test since the tiki figure moves from frame-left to frame-right, ideal for interlacing.
The first step is to double up the literal frame count. This is accomplished in one of two methods.
In order to do this properly, the new frames need to be interpolated by means of a vector-based pixel warping or morphing algorithm. This can be accomplished by a variety of different applications, including Motion 3 (by use of the Optical Flow feature), After Effects (by use of Layer > Frame Blending > Pixel Motion), Shake, the Twixtor plugin (which can be used in Final Cut Pro, After Effects and several other host applications), Boris FX, or any other application or plugin that can double the frame rate or frame count by means other than merely frame-blending the frames. You do NOT want to frame-blend this step or the entire process will not work.
The best way to tell if this step is working correctly is to look at the new frames that have been created. If they have an overlapping ghost look to them, then it's frame-blending, which you do not want. If the new frames literally look like new frames with no ghosting or overlapping, then you're on the right track.
Once your clip is rendered with twice the frame count, you'll now be ready to interlace it, which can be done in After Effects, Final Cut Pro and pretty much any other video application. I found that After Effects renders out a cleaner interlace (actually, a perfect interlace) than does Final Cut Pro, so you may want to keep that in mind. If your clip is now 30p at twice the TRT, you'll want to turn it into a 60p clip at normal speed. Here's how:
Adobe After Effects
The clip will now be 60p. Create a new 60i comp in After Effects and place the 60p clip in the timeline. Even though your timeline is only 29.97 FPS and you can't see the extra frames when scrubbing frame by frame, don't fear; when you render the final clip, it will use the extra frames in the 60p clip to create the new fields.
Let's go ahead and render this as a final clip by selecting Composition > Make Movie from the menu bar. This should open up the Render Queue window with a new comp in the queue. You'll need to change the Render Settings either by selecting a pulldown option next to it or by clicking the name next to the pulldown option.
The thing to absolutely keep in mind is to make certain you render this clip with Field Rendering turned on. You'll need to select either Upper Field First (UFF) or Lower Field First (LFF), depending on your editing hardware and format of choice. For the samples provided in this tutorial, I rendered to NTSC DV, so LFF it will be.
From there you'll want to select your format choice and render location. Click Render and you're done.
Final Cut Pro
Now when we render the clip in the FCP timeline, you have a finished 60i clip with smooth motion.
When everything is rendered correctly, you'll have an interlaced clip that's nothing short of amazing. For my testing, I used Twixtor in After Effects to perform the initial frame doubling. I then rendered the final clip using After Effects as described above and below is the result of that render. Place the clip in your DV timeline and compare it to the original 30p clip. It's next to impossible to tell that this clip was once progressive! It's easy to think that the clip was shot using an interlaced video camera (when in reality, the original clip was shot using a Canon 20D DSLR still camera, using a 60mm prime lens with a combination of time-lapse and a motorized motion rig).
There are a few ways to turn a 24p clip into a 60i (or 50i) format.
The key to this entire process lies in the frame-doubling step. The best frame-doubler will give you the best results in the end. The actual interlacing part is easy but it's the frame-doubling part where the real magic happens. Once properly interlaced, the clip will be so clean it's basically impossible to know it came from a progressive source and not an interlaced one. The results can be quite amazing to say the least.
Some plugins will allow you to re-interlace with fewer steps as listed above (e.g., RE:Vision Effects Twixtor). For the best quality, I recommend rendering the final video clip out of After Effects as opposed to your NLE if the choice is between the two.
Feel free to discuss this tutorial in Creative Cow's After Effects forum.
Marco Solorio began his career in media production at the start of the 1990's and has been accredited with many industry achievements. He's the recipient of numerous creative awards ranging from visual effects to editorial to music composition. He's a published writer for both print and web mediums and has appeared on and off-camera for both creative and technical topics. Marco owns OneRiver Media, a successful post-production facility in the San Francisco Bay Area. He also owns Cinesoft, a software company whose flagship product, Media Batch was developed as proprietary server software but is now available to the entire industry. He's also known for the internationally recognized OneRiver Media Codec Resource Site, a resource that compares various codecs for the benefit of end-users and developers alike.
: : : Page design, layout and images by Marco Solorio