Blank Video? You’re Missing a Codec.
Videos not playing? Download the appropriate codec so you can watch them.
Have you ever downloaded a video and opened it up, only to be greeted with just audio or a message saying that the video cannot be viewed? This usually means that your computer is missing a codec.
A codec, short for “coder/decoder” or compression/decompression, is a program that allows your computer to interpret video and audio. They are needed because storing “raw” video and audio is very space-prohibitive. For example, a regular audio CD is 700MB and only 74 minutes whereas equivalent MP3 are 5-20x smaller depending on the compression level. (Granted, an MP3 is a lossy format and loses detail.) A regular DVD is up to 9GB of video and surround sound audio but typical DVD “rips” are 700 to 1,500 MB.
If you’re wondering why DVDs or Blu-Rays don’t use more compression, it’s because that would require a more powerful processor to decompress/interpret the video and audio. By storing it uncompressed, the electronics inside a set-top DVD/Blu-Ray player don’t have to be as powerful and therefore are a lot cheaper.
Fortunately, over the years, most of the Internet has consolidated around a few codecs, most of which are free and open-source.
Most AVIs are encoded using Xvid/DivX (Mac, Linux, Windows): http://www.divxmovies.com/codec/
QuickTime (Mac, Windows): http://www.apple.com/quicktime/
QuickTime Alternate (Windows, a lot smaller, no iTunes): http://www.free-codecs.com/download/quicktime_alternative.htm
Windows 7 Codecs: http://shark007.net/
64-bit add-on (install along with the regular codecs): http://shark007.net/x64components.html
Flash videos (YouTube, DailyMotion, Vimeo, etc.) are FLV format and use the Flash Video Player: http://download.cnet.com/FLV-Player/3000-13632_4-10467081.html
If you run into a video file that isn’t opened by the above codecs (very rare), you can run it through MediaInfo (Mac, Linux, Windows) which will tell you what codec it’s using: http://mediainfo.sourceforge.net/en/Download
While you’re at it, consider one of the free, open-source media players that are a lot more efficient, fully-featured and more customizable than the default ones bundled with your computer:
Media Player Classic (Windows): http://mpc-hc.sourceforge.net/
VideoLAN’s VLC (Mac, Linux, Windows): http://www.videolan.org/vlc/
[Added bonus: many codecs are built-in.]
Enjoy your videos!