GRunT - Easier run-time scripting

[Gavino]

Avisynth's run-time environment is very powerful, supporting complex video processing that would be difficult or impossible to perform in a normal script. But it's not easy to use - the behaviour of run-time scripts (especially in combination) can be hard to understand and there are usability problems concerning scope and lifetime of variables.

"Cond. filters are quite complex - and sometimes I am even surprised of the outcome" - sh0dan

GRunT (Gavino's Run-Time ) is a plugin which addresses these and other problems, making the run-time system much easier to use.

Features:
- Simple, natural and robust way to pass variables into a run-time script from 'outside'
- A run-time script can be evaluated in its own independent scope
- Run-time functions can be called from a user function
- Run-time functions can be applied to any frame (relative to the current one)
- Additional variant of ConditionalFilter with single boolean expression
- Fixes a fairly serious bug in the run-time system
- Lightweight plugin extending the standard run-time environment, minimal time and memory overhead
- 100% backwards compatible with existing scripts

GRunT should be useful to anyone who uses the run-time filters, from those who make occasional use of ScriptClip to those who write complex functions based on run-time features (such as Restore24 or MRestore).

Details

The plugin provides extended versions of the following run-time filters:
- ScriptClip
- FrameEvaluate
- ConditionalFilter
- WriteFile
- WriteFileIf

The alternative names GScriptClip, GFrameEvaluate, GConditionalFilter, GWriteFile and GWriteFileIf may also be used. However, if running on version 2.57 or earlier of Avisynth, then only the alternative names may be used.
(This restriction is necessary for technical reasons - sorry about that.)

Each filter is 100% backwards compatible with its standard equivalent, but has two additional optional arguments:

• string args: the variables whose values are to be imported into the run-time script, written as a list of names separated by commas. The given variable names are evaluated in the current (compile-time) context, so can include function parameters or local variables.
  Each value becomes the initial value of the corresponding variable at each invocation of the run-time script.
• bool local: if true, the filter will evaluate its run-time script in a new variable scope, avoiding unintended sharing of variables between run-time scripts.
  Default is true if args is also specified, otherwise false (to preserve backwards compatibility).

A short example (based on the original) shows how this greatly simplifies passing function parameters into a run-time script.

function bracket_luma(clip c, float th1, float th2) {
  Assert(0 <= th1 && th1 < th2 && th2 <= 255, "Invalid thresholds!")
  ScriptClip(c, """
    avl = AverageLuma()
    avl <= th1 ? last.BlankClip() : avl >= th2 ? last.BlankClip(color=color_white) : last
  """, args="th1,th2", local=true)
}

This is much easier than the standard approach of dynamically building the runtime script using string concatenation, or passing the values via global variables.

"I really do not like this global variable business with ScriptClip ..." - stickboy

And because the run-time script is evaluated in its own scope, there is now no problem in calling bracket_luma more than once in the same script (previously the variables th1 and th2 of different instances could interfere with each other).

Elements of the args string can also take the form 'name=expression' - the expression is evaluated in the current context and is used to set the value of the named variable in the run-time script.
Example: args="x, y=n+1, c=c.Trim(2, 0)" will provide values for the variables x, y and c.
Here y need not even exist in the current environment (although x, n and c must).

The plugin also provides the following extensions to the run-time functions (eg AverageLuma):

• these functions can now be called inside a user function, when the user function is called from a run-time script
• each function has an new optional int argument, which can be used to get the value from another frame, relative to the current one. For example, AverageLuma(-1) returns the value for the previous frame. (No more assigning to current_frame ...)

For added convenience, there is a new variant of ConditionalFilter which takes a single boolean expression instead of three separate parameters as at present. This is useful when the condition to be tested is a compound one or is already available in boolean form. For example,

ConditionalFilter(c, c1, c2, \
 "AverageLuma(c1) > AverageLuma() && AverageLuma(c1) > AverageLuma(c2)")

where previously you would have to add (...,"=", "true")

Finally, the plugin fixes a fairly serious bug I discovered in the run-time system.
This fix is needed if you are running a version of Avisynth prior to build 080620 of 2.58.

More detailed documentation and examples are provided in the attached download.

EDIT 27-SEP-08: Updated to v1.0.1 to work with Avisynth 2.5.7

Comments and suggestions would still be very welcome.