javicle/docs/jvc_js.md

JVC JavaScript Expressions

JavaScript expressions are used in a couple of places in JVC.

• Operation configuration
• Operation validations

Operation Configuration

When you’re writing the JSON for an operation, many of the operation’s config parameters can be JS expressions that will be evaluated when the operation is run.

For example, say you wanted to use trim to just chop a video in half.

The start and end parameters of the trim operation support JavaScript expressions, so you could write:

{
  "comment": "cut video at midpoint",
  "operation": "trim",
  "creates": "chopped"
  "source": "some_vid",
  "end": "source.duration / 2"
}

or run:

jtrim some_vid.mp4 output_vid.mp4 0 "source.duration / 2"

In the above, source is referring to the source asset, some_vid.

When JVC loads an asset (like some_vid), or an operation creates a new asset, the asset metadata is read using mediainfo. The metadata is stored in an object that is then put into the JavaScript context using the variable name source.

Operation Validations

Once an operation completes, the validations run to ensure that the output assets pass whatever tests you want to run.

Each test is a JavaScript expressions, which is evaluated to a boolean value. If the expression is true, the test passes. If false, the test fails and the comment associated with the failing test is printed.

JavaScript Context

What variables are available in the JS context? And what properties do they have?

Assets

Assets can be defined in the JVC’s assets array, or as the output of an operation.

Assets are referenced by their asset name.