Update README.md

README.md

-node-thumbot-vtt
-================
+# Video thumbnails + WebVTT using Node.js
 
-Video thumbnail generator generating WebVTT spec file
+Thumbnails generator module. Uses [WebVTT](http://dev.w3.org/html5/webvtt/) as thumbnails descriptor. Can pack thumbnails into spritesheet using [node-sprit]() module.
+
+## Installation
+
+    npm install thumbnails-webvtt --save
+
+## Requirements
+
+* [ffmpeg](https://www.ffmpeg.org/) used by `fluent-ffmpeg` 
+* [ImageMagick](http://www.imagemagick.org/) as used by `node-sprite`
+
+## Example
+
+```javascript
+'use strict'
+
+var thumbgen = require('thumbnails-webvtt')
+
+thumbgen('/media/Hammer.of.the.Gods.2013.BluRay.720p.mkv', {
+  output:          '/vtt/Hammer.of.the.Gods.2013.BluRay.720p.vtt',
+  size:            {
+    width: 480
+  },
+  numThumbnails:   6,
+  spritesheet:     true
+}, function(err, metadata) {
+  if (err) {
+    throw err
+  }
+  
+  console.dir(metadata)
+})
+```
+
+will print
+
+```javascript
+[ { path: '/Hammer.of.the.Gods.2013.BluRay.720p/thumbnails.png#xywh=0,808,480,200',
+    from: '00:00:00.000',
+    to: '00:14:49.474' },
+  { path: '/Hammer.of.the.Gods.2013.BluRay.720p/thumbnails.png#xywh=0,0,480,200',
+    from: '00:14:49.474',
+    to: '00:29:38.947' },
+  { path: '/Hammer.of.the.Gods.2013.BluRay.720p/thumbnails.png#xywh=0,202,480,200',
+    from: '00:29:38.947',
+    to: '00:44:28.421' },
+  { path: '/Hammer.of.the.Gods.2013.BluRay.720p/thumbnails.png#xywh=0,404,480,200',
+    from: '00:44:28.421',
+    to: '00:59:17.894' },
+  { path: '/Hammer.of.the.Gods.2013.BluRay.720p/thumbnails.png#xywh=0,606,480,200',
+    from: '00:59:17.894',
+    to: '01:14:07.368' },
+  { path: '/Hammer.of.the.Gods.2013.BluRay.720p/thumbnails.png#xywh=0,1010,480,200',
+    from: '01:14:07.368',
+    to: '01:38:49.824' } ]
+```
+
+## API
+
+### thumbgen(source, options, callback)
+
+Create thumbnails (and optionally pack them into spritesheet) and create WebVTT file for file(s). Options are described below
+
+## Options
+
+* **output** defaults to `"SOURCE_DIR/SOURCE_NAME.vtt"`
+
+    * WebVTT filename
+
+* **assetsDirectory** defaults to `"SOURCE_DIR/SOURCE_NAME"`
+
+    * Name of folder which keeps thumbnails or spritesheet.
+
+* **size** defaults to `null`
+
+    * Size of generated thumbnails. If not specified original video stream `width` and `height` will be used. If only `width` or `height` is specified other will be computed according to source video ratio.
+
+* **size.width** defaults to `SOURCE_WIDTH`  
+
+    * Read above
+
+* **size.height** defaults to `SOURCE_HEIGHT`  
+
+    * Read above
+
+* **timemarks** defaults to `null`
+
+    * Array with timemarks in seconds. E.g. ['123.123', '345.345']
+
+* **numThumbnails** defaults to `null`
+
+    * Number of thumbnails to generate. Used in opposite to `timemarks`. Each thumbnail moment is calculated as `source_duration * 0.9 / numThumbnails`.
+
+* **spritesheet** defaults to `false`
+
+    * Generate spritesheet or not.
+
+* **spriteSheetName** defaults to `"thumbnails"`
+
+    * Spritesheet file name
+
+* **spriteSheetOptions** default to `null`
+
+    * Spritesheet options passed to [node-sprite](https://github.com/naltatis/node-sprite#options) `.sprite()` function.
+
+## TODO
+
+* Use cool spritesheet generator