How To Video
Make sense of digital video filesCNET's Donald Bell helps make sense of the confusing world of digital video file formats and explains some common terms and concepts.
[ Music ] ^m00:00:10 >> If you've ever tried to get a You Tube video on your iPod, or rip a DVD to your computer, you've probably come face to face with the mind boggling complexity of digital video formats. Fortunately, if you're just trying to convert video for your iPod or your Zune, there's dozens of programs out there that take the guess work out of it. But if you're curious to know what exactly makes digital video so complicated, I'm going to walk you through some common terms and concepts. Let's start with a test. What kind of digital video format is this? If you said MP4, you're logical but you're also wrong. In fact it's a trick question, since there's no way to tell the format this video's in just from looking at the file name. That MP4 extension represents the video container type. If we peek inside the file, you'll see that the videos in the H.264 format, with a 624 x 272 resolution, and audio encoded as aac. Confused? Of course you are. Here's what's going on. Let's say this sandwich bag is the video container type. In this case it's an MP4 container, but it could be any other type - like an AVI, WMV, MOV, FLV file. Hidden inside the container you're going to find the encoded video, the audio track, and maybe some extras like subtitles. Here the video's encoded using H.264 codec. But it could just as well be using anything like Divex, QuickTime, Xvid... blah, blah, blah. Same for this audio track. This one is using aac, but it could be wav or MP3 or something else. Now to play this video, whether it's on your computer, your iPhone, or your iPod, the video player needs to be able to unlock the container and decode all of the contents. But with so many elements involved, it's easy for something to go wrong. Maybe iTunes is fine with the MP4 container and the aac audio, but if the video's formatted in Divex you're screwed. To make things even more complicated, you've got things like byte rate, frame rate, and resolution; all of which can potentially break compatibility with your device. Like MP3 files, byte rate is used to describe how many bytes of data are used to describe a single second of playback. Frame rate describes how fast each frame of video will whiz past your eyes. DVD quality video range is from 25 to 30 frames per second. Finally, resolution tells you how many pixels wide and tall your video is. An HD video can be up to 1080 pixels tall or larger, but if you're just watching on an iPod, the screen size and software limitations make large video files kind of pointless. To make a long story short, byte rate, frame rate, resolution, bigger numbers are usually better but check to make sure that the device you're playing the video can support those numbers, and actually take advantage of the improved quality. Still confused? Of course you are. This stuff is enough to drive you insane. Hopefully though I've given you a better understanding of all the elements that make digital video formats so uniquely infuriating. For CNET.com I'm Donald Bell. ^m00:02:59 [ Music ]