smpte-timecode

smpte-timecode is a JavaScript library for operations with SMPTE timecodes.

Features

• usable in browser and Node environments;
• supports drop-frame and non-drop-frame codes;
• instantiate timecodes from frame count, string time code or JavaScript Date() objects;
• timecode arithmetics: adding frame counts and other timecodes;
• support of implicit conversiont to string (toString()) and number (valueOf());

Usage

const Timecode = require('smpte-timecode')
var t = Timecode('00:15:10;03');
t.add('00:02:30;00');
console.log(t.frameCount);
t.subtract(100); //frames
console.log(t.toString());

Creating Timecode() Objects

Timecode = function (timecode, frameRate, dropFrame) {...};

• timecode: number, string or Date

  • Numbers are interpreted as frame count.
  • Strings are expected as "HH:MM:SS:FF" (non-drop-frame) or "HH:MM:SS;FF" (drop-frame). The constructor will throw if the string contains invalid timecode, for example frame count above framerate or 0 frames in a drop-frame second.
  • If Date() is passed, it is converted to the timecode a master clock would have with a given framerate. Month, date and year discarded.

• frameRate: number, optional
  one of 24, 25, 29.97, 30, 50, 59.94, or 60 is expected. 29.97 is assumed if the parameter is omitted.

• dropFrame: boolean, optional
  whether the timecode is using drop-frame or non-drop-frame mode. If omitted, and timecode is a string, the drop-frame mode is determined based on the ":" or ";" characters separating the frames in the timecode parameter. If timecode parameter is not a string, drop-frame assumed for 29.97 and 59.94 framerates, non-drop-frame for all others.

Examples:

var minute = new Timecode('00:01:00:00');
var eightHundredFrames = new Timecode(800,29.97,true);
var wallClock = new Timecode(new Date());

Note: a direct call to Timecode() returns a Timecode object too, so both direct calls and instantiating with new return the same result:

console.log((new Timecode('00:15:00;00')).toString()); 
// is the same as
console.log(Timecode('00:15:00;00').toString());

Using Timecode() Objects

Once a Timecode object is created, the following member variables are available:

• frameCount: number, total number of frames
• frameRate: number, framerate in FPS
• hours: number
• minutes: number
• seconds: number
• frames: number
• dropFrame: boolean, whether timecode is drop-frame or not

The Timecode object also provides the following member functions:

• add(x): Timecode, adds x to timecode, x can be a number, Date or Timecode
• subtract(x): Timecode, subtracts x from timecode, x can be a number, Date or Timecode
• toString(): string, returns the timecode in "HH:MM:SS:FF" or "HH:MM:SS;FF" format
• toString('field'): string, returns the timecode in VITC format, where timecodes above 30fps are represented as frame.field, i.e. HH:MM:SS:FF.f
• toDate(): date, returns a Date object using today's date and timecode as wall clock
• valueOf(): number, returns this.frameCount

For more usage examples, see the unit tests.

Running Tests

To run tests, make sure you install expect.js, mocha, codecov and istanbul NPMs locally.

yarn add expect.js mocha istanbul codecov

The tests can be run in Node using:

yarn test

To run the tests in a browser environment, open the test/smpte-timecode-test.html file in a browser.

Update History

• 1.2.0
  • Added support for 59.94 fps drop-frame expressed without fields - i.e. 00:00:00;59 is 1 frame short of a second;
  • Added .ToString('field') output in HH:MM:SS;FF.f format;
• 1.1.0
  • Fixed the problem with Timecode.add(0) subtracting the frameCount for drop frame timecodes

Credits

• https://www.npmjs.com/package/timecode NPM module, which in the end I decided to rewrite. The things I needed would have been breaking changes for anyone who used it.
• http://andrewduncan.net/timecodes/ by Andrew Duncan

Legal

License: MIT
Copyright © 2017 Crystal Computer Corp.
http://www.crystalcc.com