VirtualDub documentation: A note on VirtualDub optimizations
My policy on optimizations has been to try to make as many CPU- and OS-specific optimizations dynamically dispatched. The minimum requirements for VirtualDub 1.5.2 are an 80486 CPU and Windows 95, but the program detects and uses features specific to Windows 98 and NT/2000/XP, and to CPUs that support MMX, SSE, and SSE2. As a result, you can use the general build on all systems and be confident that the program is using your CPU and OS efficiently.
One exception is the Pentium 4 build I started releasing around 1.4.11. This version is exactly the same as the regular build, except that it is compiled with the Intel C/C++ 6.0 compiler in SSE2 (P4) mode. The general build contains some optimizations for the Pentium 4 already, and the only difference in the P4 build is a few extra optimizations in C++ code that squeeze an extra 10% or so of performance out, the largest gains being in the MPEG-1 decoder code. There are no huge changes in the program to optimize for the P4 that are not already in the general build. All I do to build the P4 version is change the build target from VirtualDub - Win32 Release to VirtualDub - Win32 Release ICL.