Recent VapourSynth releases (R55+) introduced a new API version (api4) that is not compatible with the previous plugin API (api3). Even though newer VS versions can load plugins using either api3 or api4, older VS versions are stuck with api3 plugins. This poses a dilemma for (video) plugin authors:

• either you abandon users still stuck with older api3 VS versions by migrating to api4
• or, you maintain two copies (branches) of essentially the same code.

The best course of action, IMHO, is to stick with api3 to support both worlds without maintaining two copies of essentially the same code.

As anyone who has migrated video plugin from api3 to api4 would testify, there aren't that many differences between the two APIs. One might ask: is it possible to support both both API versions without duplicating code?

The answer is yes, and this project is one solution that should help with this situation.

For end users of VS plugins, this project can be used to load api4 vdieo plugins in api3 VS. (api3 VS does not have audio support, so obviously this project won't change that.)

Suppose you are stuck with VS R54, but you want to use a video plugin filter.dll that only has api4 support. You can download the released api3.dll and save it as filter.api3.dll along side with filter.dll into VS plugins directory. And then you should be able to use the filter in your api3 VS as usual.

Note for Unix users: as this process involves making multiple copies of api3.so if you have multiple api4 plugins to wrap, in order to save disk space, please use hard links instead of symbolic links.

For plugin developers, this project can help you support both api3 and api4 without any code duplication. Just migrate to api4 and include api3.cc in your project. And the rest should be automatically handled.

Examples:

• TCanny has switched to api4 recently. By using this project, we just need to slightly tweak its build workflow to make a hybrid api3/api4 filter release.
• AddGrain, similar to TCanny. We tweaked its build workflow to make a hybrid api3/api4 filter release.
• TTempSmooth, similar to TCanny. We tweaked its build workflow to make a hybrid api3/api4 filter release.
• One FFT3DFilter fork has received some significant speed optimizations, but it's only available with an api4 interface. Again, we tweaked the build workflow to produce a hybrid api3/api4 filter release.