Let me sum it up.
I did not add anything incompatible with Windows 7 to the avlib_vdplugin and VirtualDub2.1 code.
You have a problem with the official FFmpeg DLL (avcodec-61.dll), which contains components incompatible with Windows 7.
You can find more details at the link:
https://github.com/GyanD/codexffmpeg/issues/136
I didn't promise Windows 7 support to anyone. I'm not interested in this.
Windows 7 users can use one of the solutions:
1. Replace all FFmpeg DLLs with compatible ones.
For example, these FFmpeg 7.0 builds:
https://github.com/kusaanko/FFmpeg-Auto-Build/releases
2. Put the api-ms-win-core-synch-l1-2-0.dll file in the VirtualDub2.1 folder (where avcodec-61.dll is).
Link:
https://github.com/cristianadam/api-...Win7/releases/
3.Use VxKex.
Link:
https://github.com/i486/VxKex