Concepts

In JVC the main concepts are assets and operations.

The complex example illustrates just about every way to represent input assets, output assets, operation configs.

If you find yourself getting confused with some of what follows, maybe browse through that example first.

Assets

Assets are your media files: generally image, audio and video files.

All assets have a name and a path.

Input assets are defined using the assets array of a JVC spec.

For input assets, the path can be a file or a URL. URL-based assets will be downloaded to the scratch directory. This can be overridden using the dest property on the asset.

Operations produce one or more output assets, as specified in the creates property of an operation JSON object.

For output assets, the path will be within the scratch directory. You can override this using the dest property on the creates object associated with the operation.

Asset Properties

Assets expose properties that can be referenced in operations. The properties currently exposed are:

duration: duration of the audio/video in seconds (audio and video assets only)
width: width of the video in pixels (video and image assets only)
height: width of the video in pixels (video and image assets only)
aspectRatio: ratio of width / height (video and image assets only)
samplingRate: sampling rate in Hz (audio assets only)
tracks: array of tracks. only includes audio and video tracks (video assets only)
audioTracks: array of audio tracks (video assets only)
videoTracks: array of video tracks (video assets only)
assets: for a list asset, these are the nested sub-assets

Operations

Operations represent transformations to perform on the inputs, and validations to ensure correctness.

Operation Assets

An operation requires one or more input assets. These assets are referenced using the source (or for concat, sources) parameter.

An operation can produce one or more new assets, which can then be referenced in later operations.

Learn more about Asset References.

Operation Configuration

Many of the operation settings can be JavaScript expressions, for example:

"start": "someAsset.duration - 10"

The above would set the start value to ten seconds before the end of someAsset.

Learn more about JavaScript expressions in JVC.

Operation Validation

An operation may define validations to perform by defining a validation array.

Each object in the array has properties comment (to describe the test) and test which is a JavaScript expression. If it evaluates to true then the test passes. If false, the test fails and the comment is printed.