The phrase "DVR files" can refer to several types of computer files. It could refer to generic files recorded from a security system, specific files from a digital video recorder for television or a specific format used by the Windows Media Center. Which you can use and play on your PC depends on the specific format and may be restricted by law.

CCTV Footage

If you get a file with the extension .dvr, it will usually be from a closed circuit security system that records footage to a hard drive. The problem is that .dvr is not a standard format and can instead be used as an extension by different manufacturers for different recording formats. In most cases, you'll be able to only play back such files using the original recording equipment, or using proprietary software from the manufacturer. Usually you won't be able to digitally convert these files into a different video format and will instead have to do a manual conversion by connecting your original playback equipment to a video capture card on your PC and re-recording the footage.

Microsoft Format

Microsoft uses a proprietary format with the extension .dvr-ms for recordings made with its Windows Media Center software. These files will include any copyright protection included by the broadcaster, meaning you won't be able to open copyrighted ("watermarked") files on other computers or with other software. If a recording isn't copy-protected, you'll be able to play it back on any computer running Windows Media Center. You won't usually be able to play it back with non-Microsoft applications.

Television DVRs

Although television DVRs create files on a hard drive, it's not always as simple as it might seem to either put the hard drive in a computer or transfer the files and then open them on a PC. Many DVRs record using the common MPEG encoding system, but the precise format will usually be proprietary. For example, the independent software PvrExplorer Pro, which is designed to locate and copy files on a DVR hard drive, has been in development since 2006 but works only with selected Dish Network and Echostar models. Even if you can copy the files, they will often have copy protection to stop them opening on devices other than the DVR itself. For example, Dish Network allows you to move recordings to an external hard drive to expand your storage (for a fee) but the files will play back only through the DVR. Note also that a DVR's hard drive may be organized in a complicated way that makes it difficult to match a specific file to a specific recording.

TiVo Desktop

Unlike most DVRs, TiVo models explictly let you transfer files if your PC and TiVo box are on the same local network. You will need to use the dedicated TiVo Desktop software to transfer your files to the PC and to open the files. However, the video itself will play in your default media player application.

Copyright and Practical Issues

For the most part, even if you are able to copy files from a television DVR to a PC, for example as a back-up in case the DVR drive fails, you'll be able to play them back only on the DVR itself. Converting them into a format that is suitable for playback on a PC may be possible through independently-developed software, but this will depend on your brand of DVR and may vary depending on the specific model. There's no guarantee that software which claims to remove copy protection from DVR files will work and, even if it does, using such software may be a civil or criminal offense in your jurisdiction.