Added custom filter support

tests/FFMpeg/Tests/Filters/Video/CustomFilterTest.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace FFMpeg\Tests\Filters\Video;
+
+use FFMpeg\Filters\Video\CustomFilter;
+use FFMpeg\Filters\Video\FrameRateFilter;
+use FFMpeg\Tests\TestCase;
+use FFMpeg\Coordinate\FrameRate;
+
+class CustomFilterTest extends TestCase
+{
+    public function testApplyCustomFilter()
+    {
+        $video = $this->getVideoMock();
+        $format = $this->getMock('FFMpeg\Format\VideoInterface');
+
+        $filter = new CustomFilter('whatever i put would end up as a filter');
+        $this->assertEquals(array('-vf', 'whatever i put would end up as a filter'), $filter->apply($video, $format));
+    }
+}