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Online Video: File Sizes

1 March 2006 2 Comments

I'm going to continue our discussion of producing online video until someone else takes the helm of “This Week on IAOCblog.com.” Today, I'd like to talk a little about file sizes, since that is such a huge issue.

When we record an interview, we use MiniDV tape. With the camera set to record at its highest resolution, the tape will last for 30 minutes. We usually shoot interviews for about 20 minutes. When we “capture” the footage — that is, download it off the miniDV tape and onto a computer for editing — the uncut interview will be about 5 to 6 gigabytes large.

One problem with a file that large is that it will not fit onto a single CD (700 megs max) or even a DVD (4 gigs max). Files that big are very difficult to move around. When I was a refugee living in Richmond, I had all our uncut video on a single, 450-gig LaCie hard drive. To get the files to the editor, I had to hand over the hard drive. He drove to Richmond to pick up the LaCie. One client asked to see the raw video of an interview; I told her to book a ticket to New Orleans. We have no method of shipping raw video except to send a miniDV tape, which most clients can't use.

As a side note — and to illustrate the problems that can result from dealing with huge files — before I gave the hard drive to my editor, I had to pull off sensitive company data. I put that on a second external drive — but I didn't format the drive properly. A week later, the second drive crashed. Then my laptop crashed. I lost a ton of data because both computer and back-up crashed at the same time. If I didn't have to deal with huge video files, I probably never would have had such a severe crash.

I'm mentioning this because the file sizes in video will haunt you in a variety of ways. We can no longer use the best computer in our shop as a file server because it is not a good idea to edit video on a machine that is serving files to a group. File servers get a lot of traffic — coming and going — and that can cause videos to “drop frames”– to capture improperly or to crash. So now you not only need a supercomputer to edit video (we're using a PowerMac G5 with dual processors), you also have to isolate that supercomputer to some extent.

We edit our 20-minute original interview down to a 2-minute video. The file size goes from about 5 or 6 gigs to about 450 megs. The 2-minute version just fits on a CD. It can be used in a digital press kit at this point: a CD or DVD or even stored online for download by the media. This is a broadcast-quality file; television journalists can edit it into a newscast with no trouble. It is still far to big to serve online or realistically to offer to the public.

When we “render” the 450 meg, 2-minute video for the web, the file size plummets to about 4.5 megs — 100 times smaller than the high-res version, 1000 times smaller than the raw, 20-minute interview. You cannot drop a file size two orders of magnitude without losing a lot in the process. What do you lose? Frame size and clarity. Instead of being able to watch the video full screen, you get roughly the dimensions of a business card. And instead of beautiful, rich, deep textures and colors, you get splotchy-looking people whose bodies appear to be constantly reassembling. That's because they *are* constantly reassembling.

Video compression works by sampling the video and audio and then averaging the results. The screen is divided into pixels; if a pixel doesn't change much from one second to the next, then the software says, “Hey, we don't need to update that pixel.” The compression algorithm saves disk space by throwing out “minor” changes in image and sound. These sacrifices can add up to 99% of the original file size tossed out when compressed. But you lose a lot of quality. When you play one of our low-res videos (4.5 megs) full-screen, and you compare it with a high-res video (450 megs) playing full-screen from a DVD, you can really appreciate how much has been lost to compression. The blown-up low-res video looks terrible; the high-res video looks great.

We try to keep our online video files to 5 megs or less. When a client has trouble viewing their own interview, we will render the video in different formats to assist them. Recently, our 5 meg video turned into a 25 meg video just by saving it as a Windows Media file instead of a QuickTime file. The client — who could not see the 5 meg version — reported that it took her 20 minutes to download the 25 meg version. People do not want to wait 20 minutes to watch a 2-minute video.

Small file size is essential to storing, serving, and downloading online video. Small file sizes make it easier to move video from computer to iPods, cell phones, or other handheld devices. Small file sizes make it easier to share video and syndicate video. Once we produce a final version of the video, we often ask other web sites to install it. You get a lot more “yes” responses at 5 megs than you do at 500 megs.

So to summarize, expect your file sizes for online video to follow a similar trajectory from raw film, to a high-res video, to a low-res (online) video: 5000 megs to 500 megs to 5 megs. And be prepared for all the difficulties of working with large file sizes: the need for high-capacity hard drives, dedicated workstations, and brutal compression settings.

Join us Thursday afternoon, March 23, for an Online Video Workshop at the IAOC Conference in Valley Forge, PA. Register today!


  • Anonymous said:

    Thanks for the great nuts-and-bolts discussion of the realities and constraints facing an online video producer. I can see why the video i-Pod makes online video more viable: with its little screen, consumers aren't expecting the big-picture quality they'd look for on their computer screens. But what does the future hold for video? Are there bigger Internet pipes and bigger storage media around the corner that will make big files less problematic? Or will we soon see better compression that gives us small file size and high quality?
    I’m looking forward to learning more your workshop in Valley Forge.
    Don Dunnington

  • Anonymous said:

    Great explanation of compression Steve. What a lot of folks don't realize is that the television that they watch everyday on Direct TV is being compressed and uncompressed all the time. Hence, the occasional “pixilation” effect that you get. Even the HD signals that they're sending are being smashed down.
    Have you and your team experimented with online video in a flash wrapper yet? I'm curious how, if any, that effects the available size that can be viewed online.

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