Codecs and Containers

April 9, 2010

So you finally finished editing that Christmas slideshow you've been promising mom and she really, really wants to see it. If you're like most people, you probably just hit the export button and sent her whatever file your editing program spits out by default.
Usually this works just fine. But this time mom forwarded the video to Aunt Lorraine and all hell broke loose! Aunt Lorraine couldn't open the video! And it's all your fault!  And to think that she carried you for nine and a half months...
Well, it sounds like it's time for a quick lesson in video encoding.
The most popular video file formats are Quicktime (.mov) Windows Media (.wmv) and Flash (.flv). You might compare these file formats to things you can buy music on, like CD's, Records, and Cassette Tapes. Just as CD's, Records, and Cassettes can all contain audio, mov's, wmv's, and flv's can all contain audio and video. That's why these file formats are called containers. And just like you need a Record player to play a Record, you need Quicktime Player to play Quicktimes.
Of course there are exceptions to this rule: just as CD's can be played on things other than a CD player (like in a DVD player for instance), some programs other than Quicktime Player can play Quicktime files. But if Aunt Lorraine couldn't play the .mov file you sent her, the first thing you should ask her is "Do you have Quicktime Player installed on your computer?"
If she says no, then you can tell her where to go. To download it, that is. I mean she's almost 60, so you should show her a little respect. But if she says yes, she watches .mov files all the time (you nincompoop!), then well, it might have been your fault after all. That's because choosing a kind of file (i.e. a container) Aunt Lorraine can play isn't enough, you also have to choose content (that is to say, video and audio codecs) that her computer will be able to understand. And if you don't understand, then let me go back to our things you can buy music on analogy.
Here's another scenario involving you and me. Say you wanted to hear the story of Homer's Odyssey as read by Roberto Benigni (ok, so you have obscure tastes). And since you drive a 1995 Honda Odyssey, you'd be eternally grateful if I could send it to you on Cassette. So I oblige. But the next day I get a call from you asking why I sent you a tape full of gibberish? It turns out you don't understand Italian. ("It's all Greek to me" you say.) No, what you wanted was a Cassette Tape of Roberto Benigni reading Homer's Odyssey in English.
Just as you couldn't decode the greek language used to describe Homer's Odyssey, Aunt Lorraine's computer couldn't decode the particular video language (i.e. codec) used to describe your Christmas video. And just like spoken languages, there are probably hundreds of different video and audio codecs. You would need several hundred lessons in Italian to understand the tape I sent you. Luckily Aunt Lorraine's computer just needs to install the codec used in your video file. It's instant understanding. Her computer knows Kung-Fu.
Happily for us, even though there are tons of codecs out there, most programs stick to 3 or 4. It's like how most people speak either English, Spanish, Hindi, or Chinese. Currently the most popular codec for video is H.264, while mp3 and aac are quite prevalent for audio, mostly because they all can give you very good quality video and audio, at a relatively small file size.
So just remember: When someone asks you to send them a video, you'll want to know in what format and in what language. You can guess right 90% of the time, but 10% of the time they'll get nothing but gibberish.
Posted by Eric Boudreau

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