I recently wrote about coming across stock footage where the clip metadata didn’t align with the actual clip. In particular, a file may say it was shot at 23.98 frames per second, but in reality, it was shot at a different frame rate and then conformed to 23.98fps.
There are other times when the metadata lines up properly but things still go wrong. Well, maybe “wrong” is a little harsh. What I mean is that the footage doesn’t look as good as it could.
Let’s take an example of a project that runs at 29.97fps, which I’ll round up to 30 fps to make things easier to read. You have shot some scenes at 60 fps for a nice slo-mo montage.
After the first cut, you realize that you’re missing a waterfall scene that you desperately need. You don’t have time to go out and shoot, so you opt to search stock libraries to find a scene that will work. You locate a shot and download a low-res watermarked trial clip. You can tell it was shot at high speed since the slo-mo looks natural—no created frames. You buy it and download it.
Now that you have the full resolution clip, you take a closer look at it and can confirm that the metadata matches the clip. You insert it into your sequence, then move on and finish the project. Everything is great.
However, after you watch playback a few times, you notice that the stock shot jumps a bit. You look at the original file again and it looks fine. Then you notice that the clip’s codec is MJPEG (Motion JPEG) and you wonder if your workstation isn’t up to playing that back.
So you take the downloaded clip and transcode it to ProRes or DNxHD or whatever codec the rest of your footage uses. You replace the clip with the transcoded file and try again—same problem.
It’s not a codec problem, it is a frame rate mismatch problem. Although you confirmed the metadata is correct on the stock clip, that metadata tells you the clip is at 24 fps. When you place that clip on your timeline, the software “interprets” the footage to make it fit into the 30 fps sequence.
This interpretation is where the problem is. To make the clip fit, the edit software repeats a frame every 5 frames, causing the stutter that you notice.
Now the stock shot you thought would mesh perfectly with your footage doesn’t, and you’ve already purchased it.
Next time, I’ll explain how to make the shot work.
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