Tips T0017

The 4 GB File Limit
There is a lot of confusion over what is meant by the "4 GB file limit" when editing video on a PC. You do not need to understand the technical details to do video editing on a PC, but you should understand the summary given below as it might affect the tools and methods you use.

Some Basics:

• 4 GB (gigabytes) is the maximum size of a standard AVI file. A standard AVI file is called an AVI 1.0 file.
• The problem is due to the fact that standard AVI files store information inside themselves as 32 bit numbers - this gives them the range of values of about -2,000,000,000 (-2 GB) to +2,000,000,000 (+2 GB). The file itself cannot refer to anything outside this range.
• The AVI version number (1.0 or 2.0) has no connection to a DV AVI file's type (see our article on DV File Types).
• Any program that deals with AVI files by using 32 bit numbers is probably limited to using AVI files of up to 4 GB in size.

• The Video for Windows routines allow the use of 2GB AVI files.
• Carefully written programs that use Video For Windows can also use 4 GB AVI files.
• For a lot of applications, 4 GB (or even 2 GB) is plenty large enough for most uses. New digital formats like DV however generate very large files (2 GB for every 9 minutes of DV) and so there was a need to be able to deal with files greater than 4 GB.
  
  No Limits:
  The solution to the problem was to use 64 bit numbers inside the files. This has the advantages that the maximum file size is now in theory 18,000,000,000 GB, which is enough for about 150,000 years of DV video! This should be enough capacity for a while! This new AVI format is called AVI 2.0.
  AVI 2.0 is implemented in the Windows Direct Show routines, which now replace the old Video For Windows routines. Users of AVI 2.0 should note the following possible problems however:
  
  • AVI 2.0 files are not compatible with AVI 1.0 files. AVI 2.0 files cannot be used with any software that only understands AVI 1.0. Software which can handle AVI 2.0 files can also deal with AVI 1.0 files however.
  • Only Windows NT, 2000 and XP can create any file greater than 4 GB in size.
    
  The last point is important. Windows 95, 98 and ME using the FAT32 file system have a maximum file size of 4 GB of any type of file, so AVI 2.0 isn't going to help you here. Standard FAT partitions have a maximum file size of only 2GB.
  
  
  Other Solutions:
  There have been several methods that people have adopted to get around the standard AVI file size limit before AVI 2.0 appeared
  
  Non-standard AVI Formats:
  Custom AVI file formats have appeared which are proprietary to particular applications. Naturally, these non-standard AVI files can only be used with a narrow range of applications.
  
  Multiple Files:
  Large files are broken into several smaller files. This method is still a valid solution for Windows 95 and 98, where AVI 2.0 is limited to the maximum file size of the system.
  
  Summary:
  
  • Some programs are limited to a maximum file size of 2 GB for AVI files.
  • Some programs are limited to a maximum file size of 4 GB for AVI files.
  • New programs use AVI 2.0, which is effectively unlimited in size.
  • Irrespective of the AVI file format, Windows 95, 98 and ME are limited to maximum file sizes of 4 GB.
  • Windows NT, 2000 and XP allow files of effectively unlimited size