The 2 & 4 Gigabyte issue with avi files

The 2 & 4 Gigabyte issue with avi files

There seems to be a lot of confusion around this topic. I put that page online in the hope to clear things up. There are two limiting factors which are important to understand the limit. First off the avi file format by itself and second the filesystem on which the files are stored. Below you find some infromation about each of these limiting factors.

standard AVI files use internaly 32 bit pointers. One can address a maximum of 4GB using 32 bit pointers. Such files originally had SOFTWARE based limits of 1GB at the begining ( all MCI based software ), 2GB (Video for Windows oriented software) and today the theoretical maximum of this kind of avi files is 4 GB by using DirectShow based software or software which is using it's own code for reading and writing avi files.

OpenDML 1.02 compliant avi files are an extension to the standard avi files. You can think of them as a series of standard avi files stored one after the other in the same file. This is a bit oversimplified, but shoes the big picture. Such files can become as large as the filesystem in use alows files to grow.

FAT16 filesystems (if formatted under windows) can have a maximum size of 2GB and therefore can only store files up to that size. It's however possible to format a FAT16 partition of up to 4GB in size by using special software. Such filesystems then also can store files of up to 4GB in size. (that's a bit off topic, but I list it here for completness.)

FAT32 filesystems (introduced with Windows 95 OSR2, available with Windows 98, 98SE, WinME and W2K and better) can be very large. It's however NOT possible to store single files which are bigger than 4GB in size no matter what type of files they are. This is a limitation of the FAT32 filesystem.

NTFS filesystems can be up to 64 terrabytes in size. They can also store files of that size.

Out of the above you see that NTFS formatted filesystems onto which OpenDML 1.02 compliant avi files are stored don't have any limits size wise.

Since NTFS is only available with Windows NT or W2K and better you see that you need NT, W2K or any of the later Windows versions as the operating system and that you also need OpenDML 1.02 compliant software. In general this is true for DirectShow based software, but it might be also true for other software which uses it's own code to read and write avi files. A good example of the latter is VirtualDub.

Another common way to work around the 2/4GB limit is to use software which can work on a series of seamless avi files. This is having the advantage that yon don't need Windows NT/W2K or newer and or that you can work with FAT32 partitions which sometimes comes in handy. AVI_IO is an example of software which can do this.