After years of development the next major update to VapourSynth is ready. Finally Avisynth(+) is truly obsolete and the remaining 5 audio users can safely migrate.

Audio

Despite being a fairly big feature there isn’t that much to say about audio. In addition to video nodes there are now audio nodes. They mostly work like video nodes. Simple, right? So instead I’ll list the biggest points.

• Audio output with video in VFW and AVFS can be done with audionode.set_output(1). Note that these always use index 0 for video and 1 as audio source.
• Frame properties are not really a thing due to audio frames in VapourSynth being an arbitrary lump of samples. Generally you shouldn’t use them.
• Audio can’t have variable sample rate or format. Almost nobody uses variable format in video and it keeps the complexity down.

Performance

A lot of work has gone into improving performance and scripts like QTGMC can run up to 10% faster on modern CPUs. The memory usage has also been greatly reduced and a scripts like QTGMC (once again) will usually no longer reach the upper limit and warn about memory usage. Note that as a general rule script memory usage decreases with the number of plugins used that are updated to the new API version.

Compatibility and breaking changes

As usual with all big updates there are breaking changes to clean up past mistakes and remove unused features. While the core itself is more or less fully compatible with the old API a few features were removed which can cause issues with less than 1% of all plugins.

• YCoCg – never became popular and everything else treats it as degenerate YUV so now we do too)
• COMPAT formats – existed to make loading Avisynth plugins possible but in the 9 years or so since the first release Avisynth+ has appeared and just about all Avisynth filters support planar formats so it’s pointless and adds complexity to core functions)
• Many script functions were marked as obsolete or removed. The most common construct is probably vs.get_core() that no longer works. Use vs.core instead you lazy script writers! Many other functions like plugin/function enumeration were changed but the old functions simply have deprecation warnings. For now.
• Many plugins are no longer bundled/in the source tree. If your script needs subtext or histogram you have to install them yourself separately. The easiest way to do this is with vsrepo on windows.
• The alpha handling has changed and attaching the alpha as an additional frame is now the preferred method.

What this means in practice is that 99% of all plugins works properly. The only known ones that don’t work well are FFMS2 and IMWRI when outputting alpha. Update your plugins and there shouldn’t be any surprises.

For scripts it’s a bit more complicated. For example all scripts by pedantic internet users (most public scripts that is) had YCoCg support which would error out in the new version. Fortunately just about all scripts have been updated to work on both old and new VapourSynth versions. Update your scripts and there shouldn’t be any surprises here either.

Where things seem to have broken a lot is however applications that use VSScript like VSEdit. Apparently all of them used the COMPATBGR32 format because it’s convenient for output. UPDATE NOW!

Turns out floating point masks are hard. Or at least not completely intuitive so you have to make up clear rules for them. The problem solved in this version is that some filters output masks either in the 0 to 1 or -0.5 to 0.5 range for UV planes. And in turn filters that consume masks made expected one or the other. Mismatched assumptions would obviously yield garbage output or a lot of pointless offsetting using Expr.

To solve this the concept of “mask clips” have been introduced. No matter the color space they are always supposed to have a 0-1 range in floating point formats and all filters that output and consume this style of masks have been documented. MaskedMerge is probably the best example of this. Since the Invert and Binarize filters conceptually work in images and not masks (despite often being used for this) new versions called InvertMask and BinarizeMask have been introduced that will have the expected behavior in all cases.