: VirtualDub requires specific Video for Windows (VFW) compatible codecs to function. Standard DirectShow codecs used by modern players like Windows Media Player are often incompatible.
On Windows 10 or 11, try running VirtualDub in for Windows 7 or XP. Codec Problems with trying to edit videos with VirtualDub Unable To Initialize The Output Video Codec Virtualdub
Alternatively, install individual VFW codecs such as for H.264 support or ffdshow , ensuring the VFW interface is enabled in the configuration settings. Verify Configuration : : VirtualDub requires specific Video for Windows (VFW)
If using specific codecs like PICVideo MJPEG, try unchecking as this can sometimes block initialization. Use VirtualDub2 : Unable To Initialize The Output Video Codec Virtualdub