Added seekable function with DVR window

src/js/videojs-dash.js

@@ -158,10 +158,51 @@ class Html5DashJS {
     }
   }
 
+  seekable() {
+    if (this.el_.duration === Number.MAX_VALUE) {
+      if (!this.mediaPlayer_.isSeeking()) {
+        const start = this.el_.currentTime - this.mediaPlayer_.time(),
+              end = start + this.mediaPlayer_.getDVRWindowSize();
+
+        this.currSeekable_ = {
+            start: function() {
+              return start;
+            },
+            end: function() {
+              return end;
+            },
+            length: 1
+        };
+      }
+
+      if (this.currSeekable_) {
+        return this.currSeekable_;
+      }
+    }
+
+    const seekable = this.el_.seekable;
+
+    if (seekable.length > 0 && seekable.end(seekable.length-1) === Number.MAX_VALUE) {
+      return {
+        start: function() {
+          return 0;
+        },
+        end: function() {
+          return Infinity;
+        },
+        length: 1
+      };
+    } else {
+      return seekable;
+    }
+  }
+
   duration() {
     const duration = this.el_.duration;
+
     if (duration === Number.MAX_VALUE) {
-      return Infinity;
+      const dvrWindowSize = this.mediaPlayer_.getDVRWindowSize();
+      return (dvrWindowSize) ? dvrWindowSize : Infinity;
     }
     return duration;
   }