Javicle - a JSON Video Composition Language

JVCL (pronounced “Javicle”) is a JSON DSL for audio/video transformations.

Under the hood, it’s all shell commands: ffmpeg, mediainfo and so on.

JVCL provides higher-level semantics for working with these lower level tools.

Motivation

I don’t do much video editing, so I’ve never bothered to learn iMovie or any graphical video editor. My editing needs are usually pretty simple, so I bust out ffmpeg and get it done.

But it seems like every time, there is at least one wrinkle in my requirements that requires some deep research into ffmpeg filter arcana and before I know it, the day is done.

I created JVCL to make it really easy to do the most common things people usually do to videos: splitting, concatenating, letterboxing, overlaying one video onto another, and so on.

A Quick Example

Suppose you have one video that is five minutes long, and you want to split it into five videos, each one minute long.

With ffmpeg and bash, you might do something like this:

    INCR=60
    for ((i=0;i<300;i=(i+INCR))); do
      ffmpeg -i /tmp/my/source.mp4 -ss ${i} -t $((i+INCR)) /tmp/my/slice_${i}_$((i+INCR)).mp4
    done

With JVCL, you’d write this spec file and save it to a file (for example my-spec.jvcl):

{
  "assets": [ {"name": "src", "path": "/tmp/my/source.mp4"} ],
  "operations": [{
      "operation": "split",
      "creates": "src_split_files",
      "source": "src",
      "interval": "60"
  }]
}

and then run it like this:

jvcl my-spec.jvcl

Yes, the JVCL is longer, but I think many would agree it is easier to read and maintain.

As the number of media assets and operations grows, hand-crafted shell scripts with magical ffmpeg incantations become ever more inscrutable.

JVCL is designed for readability and maintainability. JVCL will continue to evolve towards greater coverage of the full capabilities of ffmpeg.

Who is JVCL not for?

If you like GUIs, JVCL is probably not for you.

JVCL is not a replacement for Final Cut Pro or even iMovie.

Who is JVCL for?

JVCL is for people who like CLIs and automation.

JVCL is for people with relatively simple video composition needs (for now), since the range of operations supported is limited.

Requirements

• Java 11
• Maven 3

The first time you run jvcl, it will automatically build the JVCL jar file from sources, using maven and javac. This takes a little time but only needs to be done once.

Running JVCL

Learn more about running jvcl and other useful tools.

JVCL Concepts

Learn about Assets and Operations, the core concepts of JVCL.

Supported Operations

Today, JVCL supports several basic operations.

For each operation listed below, the header links to an example from the JVCL test suite.

concat

Concatenate audio/video assets together into one asset.

ken-burns

For transforming still images into video via a fade-pan (aka Ken Burns) effect.

letterbox

Transform a video from one size to another size, maintaining the aspect ratio of the video and adding letterboxes on the sides or top/bottom. Handy for embedding mobile videos into other screen formats.

overlay

Overlay one asset onto another.

remove-track

Remove a track from a video asset.

scale

Scale a video asset from one size to another. Scaling can be proportional or anamorphic.

split

Split an audio/video asset into multiple assets of equal time lengths.

trim

Trim audio/video; crop a section of an asset, becomes a new asset.

Complex Example

Here is a long, complex example that uses every operation.

What’s with the name?

A cross between a javelin and an icicle? Does that have any positive connotations? I really don’t like naming things.