javicle/README.md

# Javicle - a JSON Video Composition Language
Javicle (JVC for short) is a JSON DSL for audio/video transformations.

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

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

# Motivation
I infrequently find myself doing 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 the
job done.

But it seems like every time, there is at least one wrinkle in the requirements
that requires some deep research into
[ffmpeg filter arcana](https://ffmpeg.org/ffmpeg-filters.html).

Hours later, before I know it, the day has gone by.

I created JVC 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:
```shell script
    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 JVC, you'd write this spec file and save it to a file
(for example `my-spec.jvc`):
```json
{
  "assets": [ {"name": "src", "path": "/tmp/my/source.mp4"} ],
  "operations": [{
      "operation": "split",
      "creates": "src_split_files",
      "source": "src",
      "interval": "60",
      "validate": [{ "comment": "expected 12 files", "test": "output.length === 12" }]
  }]
}
```
and then run it like this:
```shell script
jvc my-spec.jvc
```
Yes, the JVC is longer, but I think many would agree it is easier to read
and maintain.

As you can see above, JVC can also `validate` your operations to ensure that
the output assets are what you expect them to be.

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

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

# Who is JVC not for?
If you like GUIs, JVC is probably not for you.

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

# Who is JVC for?
JVC is for people who like CLIs and automation.

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

JVC is for people who have used ffmpeg filters before and had flashbacks
of editing Sendmail configs, debugging PostScript, or maintaining a legacy
Perl system.

##### Caveat Emptor
Obligatory Disclaimer: JVC is still relatively new software and lots of stuff
might not work right, ffmpeg could crap out on bad arguments, encodings,
formats, filter syntax errors, or whatever.

In any case, JVC should never overwrite your source files, since all output
goes to new files.

# Requirements
 * Java 11
 * Maven 3

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

# Running JVC
Learn more about **[running `jvc`](docs/running.md)** and other useful tools.

# JVC Concepts
Learn about **[Assets and Operations](docs/concepts.md)**, the core concepts
of JVC.

# Supported Operations
Today, JVC supports several basic operations.

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

### [add-silence](src/test/resources/tests/test_add_silence.jvc)
Add a silent audio track to a video asset.

### [adjust-speed](src/test/resources/tests/test_adjust_speed.jvc)
Speed up or slow down a video asset. Sound can be silenced, played at
regular speed, or sped up/slowed down to match the video.

### [concat](src/test/resources/tests/test_concat.jvc)
Concatenate audio/video assets together into one asset.

### [ken-burns](src/test/resources/tests/test_ken_burns.jvc)
Transform a still image into video via a zoom-pan (aka Ken Burns) effect.

### [letterbox](src/test/resources/tests/test_letterbox.jvc)
Resize a video, maintaining the aspect ratio and adding letterboxes on
the sides or top/bottom.

### [merge-audio](src/test/resources/tests/test_merge_audio.jvc)
Merge an audio asset into the audio track of a video asset.

### [overlay](src/test/resources/tests/test_overlay.jvc)
Overlay one video onto another.

### [remove-track](src/test/resources/tests/test_remove_track.jvc)
Remove a track from a video asset.

### [scale](src/test/resources/tests/test_scale.jvc)
Scale a video asset from one size to another. Scaling can be proportional
or anamorphic.

### [split](src/test/resources/tests/test_split.jvc)
Split an audio/video asset into multiple assets of equal time lengths.

### [trim](src/test/resources/tests/test_trim.jvc)
Trim audio/video; crop a section of an asset, becomes a new asset.

## Complex Example
Here is a [long, complex example](docs/complex_example.md) that uses
every operation.

## JVC JavaScript Expressions
There are actually two DSLs in JVC. One is the JSON format for JVC files,
which tells jvc where the assets are and what to do with them.

The second DSL is not really a full DSL, it's more a JavaScript context
in which you can evaluate expressions.

## What's with the name?
A cross between a javelin and an icicle? JSON and a miracle?
Something with positive connotations?
I really don't like naming things.