What Is a CAP File?

A file with the CAP file extension is most likely a Packet Capture file created by packet sniffing programs. This kind of CAP file holds raw data collected by the sniffing program so that it can be analyzed at a later time or with a different program.

Some CAP files might instead be Construct Game Development files. These CAP files are project files for DirectX games created with the Scirra Construct game editing software.

They can contain sounds, graphics, models, and other things used by the game.

ASUS uses CAP files too, as a BIOS Update file. These files are used to update the BIOS on ASUS brand motherboards.

CAP is also a subtitle/caption file format that stores text meant to be played along with a video. It's used by some broadcasting companies and might be called a Videotron Lambda file.

How to Open a CAP File

CAP files that are Packet Capture files can be opened with the free Wireshark or Microsoft Network Monitor program. Some other applications that supporting opening a .CAP file include NetScout's Sniffer Analysis and Klos PacketView Pro, and I'm sure there are others.

Scirra Construct is probably your best bet if your CAP file is a Construct Game Development file.

ASUS BIOS Update files that are in the CAP file format are used to update the BIOS only on ASUS motherboards. Go here to see how to access the BIOS on your ASUS motherboard.

The ASUS Support website has additional information if you need specific help on using the CAP file.

Subtitles that are in the Videotron Lambda file format can be opened with the SST G1 subtitling software.

Tip: You might be able to use use Notepad, Notepad++, or another text editor to open your CAP file.

Many files are text-only files meaning no matter the file extension, a text editor may be able to properly display the file's contents. This may or may not be the case with your specific CAP file but it's worth a try.

Considering the various types of CAP files there are, and that several different programs might be involved depending on the actual format being used in the file, you may find that the program Windows tries to use to open CAP-type files isn't the one you'd like. See my How to Change the Default Program for a Specific File Extension piece for help fixing that problem.

How to Convert a CAP File

You can convert a Packet Capture file to HCCAP with hashcat, or to .CSV, .TXT, .PSML (XML Packet Summary), .PDML (XML Packet Detail), or .C (C Arrays Packet Bytes) with Wireshark.

To convert a CAP file with Wireshark, you have to first open the file through the File > Open menu, and then use the File > Export Packet Dissections menu option to choose an output format.

There is no reason I'm aware of that makes sense to convert a Construct Game Development file or a BIOS Update file to another format.

Subtitles ending in the CAP file extension can be converted to TXT, PAC, STL, SCR, and other file formats, using the SST G1 program mentioned above.