Formats and Codecs (page 2)

While audio takes up a much smaller amount of data on a typical project compared to video, it still bears discussion since, of course, half of the experience of a video presentation is audio. It's also easier for pretty much any device (whether a computer, a camcorder, a playback device, etc.) to process audio than video, regardless of the levels of compression in use.

Take a simple linear PCM file that you'd get if you captured some footage from a Mini DV tape and then separated the audio from the video. This is pretty much the most raw, unprocessed form of audio that you can get. Practically any computer can process linear PCM quickly with reckless abandon - the longest part of the operation would be the time needed by the hard drive to read the file into the system.

On the other hand, before compressed audio can be edited further, the computer has to decompress it. If you, opened, say, an MP3 file in Audacity, the needed operation would happen up-front before you could actually start editing the audio.

Another differentiating factor between audio formats is the ability to encode more than just two channels of audio. Most producers working on 5.1-channel audio mixes will encode them into the Dolby Digital format. This has become the de facto standard for digital surround-sound mixes over the years, mostly as a result of being one of the two mandatory audio formats for DVD.

You know all those QuickTime and AVI files strewn about your hard drive - at the core level, they're all the same, right? Well... not quite. There's a bit more going on.

Take another look at the export settings screen of your editing software. Under both AVI and QuickTime, you'll see a number of compressors other than the good ol' reliable DV codec. There are a lot of choices you can make and a lot of options at your fingertips (so tread carefully!). This is also the reason why there's generally no guarantee that you can play an AVI file interchangeably in any system you might bring it to. Generally, QuickTime's codec management tends to be more robust, so it's usually more likely that a QuickTime file can play the first time on a computer. While a particular MOV file might include Sorenson video and MP3 audio, another might include DV video and linear PCM audio. Same goes with AVI.

Both AVI and QuickTime are wrapper formats, also known as container formats. The goal of a wrapper is to be a holding tank for video and audio packets, which are multiplexed together so the program inside can be read by the computer in a logical order.

MPEG program streams are also worth mentioning here, as they are used in a modified form on DVDs. The VOB files on DVDs are little more than MPEG program streams, though they often include subtitles and CSS encryption (particularly if the VOB in question was on a Hollywood-distributed title).

Two other wrapper up-and-coming formats that include Matroska, an open-source wrapper format, and MXF (Material eXchange Format), a professional wrapper format that is used by high-end Avid editing systems and Sony's XDCAM system. You most commonly find Matroska as a distribution wrapper format, and MXF hasn't begun to trickle into many prosumer editing workflows quite yet.

We hope to have assisted you in understanding how codecs and formats impact your daily life as a video producer. There's a lot here and things are evolving, as does everything else in our field.

Charles Fulton is Videomaker's associate editor.

Although we're magazine editors, we are fellow consumers along with our audience. As such, we are tremendously disappointed that another format war is taking place in HD disc formats. HD DVD and Blu-ray Disc are currently slugging it out in the marketing and retail arenas. (Ed. Note: At press time, Warner announced it is planning to switch from HD DVD to Blu-ray Disc, so many voices we hear are now declaring Blu-ray Disc the winner.) We had hoped that all of the manufacturers would have figured out that consumers generally roll their eyes when there's a prospect of choosing the wrong format (remember how VCR sales were slow until VHS killed off the consumer version of Beta?).

This isn't the first format war we've seen lately, particularly as far as the DVD Forum is concerned. The DVD-R vs. DVD+R fracas from a few years ago was resolved relatively quietly, with the benefit of pretty much all burners now being able to handle either type of media. And the DVD-Audio vs. Super Audio CD war has pretty much fizzled (unless you happen to be talking to a hardcore audiophile). Neither format was adopted widely - the humble CD sounds just fine to pretty much everyone we know. (Yes, we know that some of you still prefer LPs... good for you.)

Then again, there's recently been a lot of chatter about how the 1-2 punch of even-more-refined compression algorithms and ever-faster broadband Internet access might completely eliminate the need or want for a HD disc format at all, rendering the whole discussion moot. The sooner, the better, we say.

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