Wow! I Didn't Know That…

Posted on by Larry

The good folks at Accusys sent me an 8-drive RAID to test recently. (You can read my review of their ExaSAN A08S-PS unit in the next issue of my newsletter; coming out later this month.)

However, what I want to share with you today was something I discovered during my testing that totally surprised me.

Video editing is the most difficult thing we can do on a personal computer, because it requires really top-notch gear and editing software to all mesh perfectly in order to get any work done.

But what REALLY pushes your system to the limit is multicam editing. Working with more than two or three streams of simultaneous video truly separates the weak from the strong, from a hard disk point of view.

So, I decided to test this RAID by editing some 720p/60 P2 (DVCPROHD) footage with it.

NOTE: A quick technical note. DVCPROHD requires a data transfer rate from your hard disk to your computer of about 15 MB/second in order to display video in real-time. So, two streams of P2 video require about 30 MB/second. The key number to watch in the charts below is the READ number.

FireWire 800 drives can deliver up to about 80 MB/second of data; which means they are limited to about five streams of HD video. In practical terms, they may play less, depending upon the video format.

Screen shot

So, I created a multiclip containing 10 DVCPROHD clips, edited it into the Timeline, and started to switch between shots during playback by clicking the appropriate image in the Viewer.

NOTE: All the images match because, for simplicity, I took one image and duplicated it. These are all separate video files, not aliases pointing to the same file.

Screen shot

ONE CLICK and I got the dreaded “Dropped Frame” warning. (I hate this thing!)


So, I scaled back the number of clips in the multiclip to six, and everything worked perfectly.

But, what’s the sense of spending all the money to buy a fast RAID if it only does six streams of HD video.

NOTE: And if THAT isn’t a snobbish sentence, I don’t know what is. Imagine what you would have paid ten years ago to edit six real-time streams of HD video. You would have KILLED for the chance. Today, pffft…, can’t be bothered.

Then, as I was about to give it up as a bad job, a little voice in my head said: “Larry, what happens if you edit using keyboard shortcuts?”

So, I selected Tools > Keyboard Layout > Multi-camera Editing. This allows me to use the numeric keyboard to switch between cameras.

Six streams of 720p60 HD worked perfectly. (Which I would expect, since it worked in the Viewer.)

But TEN streams of 720p60 HD also worked perfectly, provided I use the keyboard shortcuts. And this I did NOT expect. I would have expected the same performance from the keyboard shortcuts as I would in the Viewer.

Screen shot

So then I tried 16 streams of 720p60 HD video. Worked PERFECTLY using keyboard shortcuts!

Screen shot

Even though running 16 streams requires Read speeds of 231 MB/second from the RAID; far more than I could get from a single drive.

Hmm… Time to get serious about this.

Screen shot

I transcoded 22 clips of 1920×1080 60 fps AVCHD into ProRes 422. ProRes 422 requires 17.4 MB/sec, at a minimum, for real-time playback of a single 1080p HD stream. The images are gorgeous, but the files are not small.

I linked all 22 clips together, turned off the display of six tracks (because a multiclip in FCP only displays 16 tracks at one time).

NOTE: There’s that snobbery again… ONLY 16 tracks of real-time full-res HD clips…! Sheesh…

Screen shot

There they are. (Thanks, Joe Centeno, for the video!)

Screen shot

WOW! 271 MB/sec. Playing smoothly and editing perfectly — and I was editing to a new shot about once a second, with ZERO dropped frames. Perfect playback!!

Holy Smoke! I did not expect this.

So, here’s the key thought. The next time you are editing multicam work, make it a point to use the keyboard shortcuts. You’ll be stunned at how much easier this is and how few dropped frames you experience.

And having a fast RAID is critical when you start editing more than four streams of video.


P.S. Here’s a short video tutorial, available in my store, that shows how to create and edit Multiclips using the Viewer, keyboard shortcuts, and buttons.

6 Responses to Wow! I Didn't Know That…

  1. Methinks you’ve uncovered a big juicy bug? How is the RAID conflicting with your pointing device? Peeking at the website for Accusys it seems to me you should have gotten way better performance if you had the 5GBs PCIe 2.0 interface. Do you have the latest and greatest Mac? Something is bottle-necking big time. The web site claims you can do 25 streams of Pro Res 4444! and does not say anything about please don’t use a mouse .

    • Larry says:


      I don’t think it’s a bug. First, ProRes 422 only needs about 17.4 MB/sec of data per stream. So, 16 streams would require about 280 MB/sec from the RAID. There’s no reason for the RAID to go faster in this instance, though it can; its just that FCP does not require more speed for this multiclip.

      Second, while Accusys website may say it supports 22 streams of ProRes 4444 video, Final Cut does not. FCP only supports 16 streams of video, regardless of format. Also the size of ProRes 4444 files totally depends upon the amount of transparency data in the clip. I would be cautious in accepting this particular statement.

      Third, I think you have a “B” in the wrong position. I don’t know anything that will deliver 5 GB/s of data (5 GigaBYTES). However, 5 Gb/s (5 GigaBITS) is more reasonable. And 5Gb/s converts to 625 MB/sec, which was within shouting distance of what I was seeing.

      Fourth, I ABSOLUTELY do not think this is an Accusys problem. This is completely a Final Cut issue — and one that I had not discovered before. In this particular case, I believe Accusys is blameless.


  2. Whoops! Yup, that ought to have been bits, not Bytes, still more bandwidth capacity available than you were utilizing.

    Have you replicated this or a similar scenario with another brand of RAID? That would point the finger squarely at FCP!

    If a power user were ever actually to perform this kind of multi-cam editing they’d probably be a keyboard shortcut jockey anyway, perhaps that’s why this FCP bug has never surfaced before. Congrats!

  3. Skip Hall says:

    This really is interesting, considering that the polar opposite was true in my last version of FCP running on my G5. In that version, trying to change the angles by using the keys on the numeric pad would not work at all. The only way to reliably change from one angle to the next was to use the mouse and click on the frame in the Viewer. The keyboard shortcuts never seemed to work properly. Interesting, huh?

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