introduce secondsPerThumbnail and framesPerThumbnail

README.md

@@ -89,10 +89,18 @@ Create thumbnails (and optionally pack them into spritesheet) and create WebVTT
 
     * Array with timemarks in seconds. E.g. ['123.123', '345.345']
 
-* **numThumbnails** defaults to `null`
+* **numThumbnails** defaults to `0`
 
     * Number of thumbnails to generate. Used in opposite to `timemarks`. Each thumbnail moment is calculated as `source_duration * 0.9 / numThumbnails`.
 
+* **secondsPerThumbnail** defaults to `0`
+
+    * If specified thumbnails will be generated each `secondsPerThumbnail` seconds.
+
+* **framesPerThumbnail** defaults to `0`
+
+    * If specified thumbnails will be generated each `framesPerThumbnail` frames.
+
 * **spritesheet** defaults to `false`
 
     * Generate spritesheet or not.

lib/index.js

@@ -27,8 +27,8 @@ module.exports = function(source, options, callback) {
   if (!source) {
     return callback(new Error('Source video file is not specified'))
   }
-  else if (!options.numThumbnails && !options.timemarks) {
-    return callback(new Error('You should specify either timemarks or number of thumbnails to generate'))
+  else if (!options.numThumbnails && !options.secondsPerThumbnail && !options.framesPerThumbnail && !options.timemarks) {
+    return callback(new Error('You should specify the way timemarks are calculated'))
   }
 
   var sourceExt = path.extname(source)
@@ -58,18 +58,53 @@ module.exports = function(source, options, callback) {
     metadata = data
 
     if (!options.timemarks) {
-      var diff = metadata.duration * 0.9 / options.numThumbnails
-        , i = 0
-
       options.timemarks = []
+    }
     options.bounds = []
 
+    var mark
+      , i = 0
+
+    if (options.timemarks.length) {
+      i = 0
+      while (mark = options.timemarks[i++]) {
+        options.bounds.push(mark)
+      }
+    }
+    else if (options.numThumbnails) {
+      var diff = metadata.duration * 0.9 / options.numThumbnails
+      i = 0
+
       while (i < options.numThumbnails) {
         options.bounds.push(Number(i*diff).toFixed(3))
         options.timemarks.push(Number(i * diff + diff / 2).toFixed(3))
         i++
       }
     }
+    else if (options.secondsPerThumbnail) {
+      mark = 0
+
+      while (mark < metadata.duration) {
+        options.bounds.push(Number(mark).toFixed(3))
+        options.timemarks.push(Number(mark).toFixed(3))
+
+        mark += options.secondsPerThumbnail
+      }
+    }
+    else if (options.framesPerThumbnail) {
+      mark = 0
+
+      while (mark < metadata.duration) {
+        options.bounds.push(Number(mark).toFixed(3))
+        options.timemarks.push(Number(mark).toFixed(3))
+
+        if (!metadata.fps) {
+          return callback(new Error('Can\'t determine video FPS.'))
+        }
+
+        mark += options.framesPerThumbnail / metadata.fps
+      }
+    }
 
     if (!options.size) {
       options.size = {

lib/utils.js

@@ -80,7 +80,8 @@ exports.metadata = function(source, callback) {
         return callback(null, {
           duration: parseFloat(metadata.format.duration),
           width:    parseInt(stream.width, 10),
-          height:   parseInt(stream.height, 10)
+          height:   parseInt(stream.height, 10),
+          fps:      parseInt((stream.r_frame_rate || stream.avg_frame_rate).replace(/\/1/, ''), 10)
         })
       }
     }