If using specific codecs like PICVideo MJPEG, try unchecking as this can sometimes block initialization. Use VirtualDub2 :
: If you are using a 64-bit version of VirtualDub, you must have the 64-bit version of the codec installed. A 32-bit codec will not be visible to a 64-bit instance of the software. Unable To Initialize The Output Video Codec Virtualdub
The newer VirtualDub2 includes built-in support for more modern containers and codecs, which often bypasses the initialization issues found in older variants. : If using specific codecs like PICVideo MJPEG, try
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 : Unable To Initialize The Output Video Codec Virtualdub