As most folk around me, I was bothered by the different video formats.I have differently formatted files stored in you PC,and not every palyer support all the formats.So I afford nearlly all of my day online for the answer,and hope my pleasant can share with those who cannot distinguish the diverse video formats.
Video formats are classified into two applications, one for local use and the other for Internet. The formats for local use include AVI, nAVI, WMA,MPEG suite, RM,MOV, etc. What the differences between these formats?
The AVI (Audio Video Interleave) format was developed by Microsoft. AVI has such advantages as high image quality, application in multi-platforms. But its disadvantages are also explicit, large volume, without a unified compression standard, and the most common nuisance is that the higher-version Windows Media Player simply can’t play AVI videos which are edited with earlier codes, and vise versa.
The AVI format is supported by all computers running Windows, and by all the most popular web browsers. It is a very common format on the Internet, but not always possible to play on non-Windows computers.
Videos stored in the AVI format have the extension .avi.
nAVI(new AVI),a new kind of video format. Don’t mistake it for the brother of AVI, and in fact the two has little relationship. nAVI is a variation of compression arithmetic ASF, but still a bit distinct from it. By increasing frame rate, nAVI enhances definition of ASF videos, but at the cost of the streaming attribute of ASF video files.
The Windows Media format is developed by Microsoft.
Windows Media is a common format on the Internet, but Windows Media movies cannot be played on non-Windows computer without an extra (free) component installed. Some later Windows Media movies cannot play at all on non-Windows computers because no player is available.
Videos stored in the Windows Media format have the extension .wmv

The MPEG (Moving Pictures Expert Group) format is the most popular format on the Internet. It is cross-platform, and  supported by all the most popular web browsers.
Videos stored in the MPEG format have the extension .mpg or .mpeg
The RealVideo format was developed for the Internet by Real Media.
The format allows streaming of video (on-line video, Internet TV) with low bandwidths. Because of the low bandwidth priority, quality is often reduced.
Videos stored in the RealVideo format have the extension .rm or .ram.

MOV:The QuickTime format is developed by Apple.
QuickTime is a common format on the Internet, but QuickTime movies cannot be played on a Windows computer without an extra (free) component installed.
Videos stored in the QuickTime format have the extension .mov.
You can go the website for more information http://www.webopedia.com/Multimedia/Video/Video_Formats/
If you have so many different formats in your Pc as me,if you wanna transfer them from your PC to your mp3/mp4/ipod,you need an converter.If you are not familiar with video converters,you can click here
or shareware  have a view.