[QuaddiMM]

Originally Posted by squid_80

I had a quick look at the code, the only thing I'd comment on is I don't think it's worth implementing a cache since avisynth will already do that for you. It does crash the same as mine with the latest 2.5 beta, I haven't tried 2.6.

Yeah - but the avisynth-cache only works for frames that were already returned by GetFrame. This doesn't cover 'prefetched' frames, so there is a cache for them.
EDIT: That's actually wrong. You're right about the cache. I could omit it.

But currently all frames are put in the cache, even those explicitly requested. I did that for it was the easiest way to do. I'm new to the threading-stuff and it confuses me, so I kept it easy.

I don't see how non-threadsafe filters are a problem as long as getframe calls for individual filters are serialized, which is the point here - a filter doesn't process multiple frames in parallel, instead multiple filters run in parallel processing different frames.

That's the point. I thought I avoided thread-safety issues by only requesting one frame at a time. There I was wrong or it's an error in the code.

What would be cool is to have code that analyzes which frames are being requested and adapts, rather than assuming linear access.

That would be very hard to do properly. For encoding, linear prefetching should be enough.

Originally Posted by MfA

With processes a separate instance of the filter will always have it's own set of variables, re-entrance and thread-safety are only an issue with shared resources and multithreading. Things can still go wrong in other ways with concurrent programs, but that is neither here nor there.

With multiprocessing every filter can be run in parallel with other instances of itself, unless the developer really tried very hard to break things (for instance by using named win32 objects as a sidechannel for passing data between filters ... not that many filters using sidechannels though, maybe mvtools?).

Sorry, I got you wrong there. So you mean not just using different processes, but also running different instances of the filters. That may solve some problems. But it's more interesting for MT-plugin as it really runs the same filter twice at the same time.