I use the excellent Firestore device sometimes when I’m shooting video with my Canon XL2. It provides up to 7 hours of runtime (along with the excellent PowerBagJunior battery) and allows me to quickly edit video without dealing with tape.
However, a few months ago I noticed that an update to Final Cut Pro (or maybe Quicktime) broke my workflow. The Firestore segments its recorded video into <2GB chunks (which is about 9 minutes of video). This isn’t much of a hassle because it’s easy to drop them all into a Final Cut Pro timeline and have them automatically line up. But at some point a few months ago, I noticed that there were very short (1-2 frame) gaps appearing in the audio at each join in the timeline. Needless to say, this was very disconcerting. Try as I might, I could not get anybody interested in this (not Focus, not Apple…nobody). I could not believe it was my problem.
So this week it bit me again, and this time I decided to revert to my old debugging chops from Back In The Day when I used to be a fearsome software coder with a reputation for leaving no bug unturned (or something like that).
Suffice it to say, this was difficult to figure out, but I’ve finally gotten to the bottom of the problem, found a solution (albeit a clunky one), and figured out how to get a few more years of use out of my Firestore.
In a nutshell, the Firestore is recording my Canon XL2’s “24P” video at the “drop frame” rate of 23.98 frames per second. Quicktime Pro’s player says “that’s fine” and plays it seamlessly, as do most other Quicktime applications. But Final Cut Pro sees the 1-2 frame gap in the audio. Why? Because the actual framerate of “24P” dropframe video is 23.976 frames per second, not 23.98. And for some reason, the Quicktime applications don’t seem to care. But Final Cut Pro is obviously far more fussy, and assumes the Quicktime file is 100% accurate, and in this case, it’s wrong. That’s because the audio is actually 23.976 frames per second (4/1000 of a second shorter) than the video, which is 23.98 frames per second. Over the space of the 9+ minutes of a segment of video on the Firestore, that means the audio actually ends a fraction of a second earlier than the video, causing the gap.
So, the right way to fix this problem would be for the Firestore’s manufacturer to fix this bug in their device. I’m not too sure they’d be interested in doing that because they’ve since moved on to newer Firestore devices. However, I wonder if this bug is also in their newer devices. Hmm…
Anyway, here’s the clunky fix I found. There’s a nice little Quicktime player application called QT Sync (get it here: http://www.qtsync.com/qtsync.php) that is capable of directly editing a Quicktime movie file and changing the frame rate. This is a non-destructive change, as this just changes a notation in the file itself. However, now the movie file has two extra blank frames at the end. So when you drag it into Final Cut Pro’s timeline, you have to carefully trim off the last two video and audio frames.
I hope this proves helpful.