diff --git a/src/FFMpeg/Format/DefaultFormat.php b/src/FFMpeg/Format/DefaultFormat.php
index f763161..6f4ccdb 100644
--- a/src/FFMpeg/Format/DefaultFormat.php
+++ b/src/FFMpeg/Format/DefaultFormat.php
@@ -21,7 +21,7 @@ abstract class DefaultFormat implements Format
 
     public function getExtraParams()
     {
-
+        return '';
     }
 
     public function getWidth()
@@ -133,6 +133,11 @@ abstract class DefaultFormat implements Format
 
     public function setGOPsize($GOPsize)
     {
+        if ($GOPsize < 1)
+        {
+            throw new \InvalidArgumentException('Wrong GOP size value');
+        }
+
         $this->GOPsize = (int) $GOPsize;
     }
 
diff --git a/tests/src/FFMpeg/Format/DefaultFormatTest.php b/tests/src/FFMpeg/Format/DefaultFormatTest.php
new file mode 100644
index 0000000..2426fe2
--- /dev/null
+++ b/tests/src/FFMpeg/Format/DefaultFormatTest.php
@@ -0,0 +1,314 @@
+<?php
+
+namespace FFMpeg\Format;
+
+require_once dirname(__FILE__) . '/../../../../src/FFMpeg/Format/DefaultFormat.php';
+
+/**
+ * Test class for DefaultFormat.
+ * Generated by PHPUnit on 2012-04-13 at 11:03:02.
+ */
+class DefaultFormatTest extends \PHPUnit_Framework_TestCase
+{
+
+    /**
+     * @var DefaultFormat
+     */
+    protected $object;
+
+    protected function setUp()
+    {
+        $this->object = new DefaultFormatTester(320, 240);
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::__construct
+     * @covers FFMpeg\Format\DefaultFormat::getWidth
+     * @covers FFMpeg\Format\DefaultFormat::getHeight
+     */
+    public function testConstruct()
+    {
+        $this->assertEquals(320, $this->object->getWidth());
+        $this->assertEquals(240, $this->object->getHeight());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getExtraParams
+     */
+    public function testGetExtraParams()
+    {
+        $this->assertEquals('-f format', $this->object->getExtraParams());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setDimensions
+     */
+    public function testSetDimensions()
+    {
+        $this->object->setDimensions(240, 640);
+        $this->assertEquals(240, $this->object->getWidth());
+        $this->assertEquals(640, $this->object->getHeight());
+
+        $this->object->setDimensions(242, 638);
+        $this->assertEquals(240, $this->object->getWidth());
+        $this->assertEquals(640, $this->object->getHeight());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setDimensions
+     * @dataProvider getWrongDimensions
+     * @expectedException \InvalidArgumentException
+     */
+    public function testWrongDimensions($width, $height)
+    {
+        $this->object->setDimensions($width, $height);
+    }
+
+    /**
+     * Data provider for testWrongDimensions
+     *
+     * @return array
+     */
+    public function getWrongDimensions()
+    {
+        return array(
+          array(0, 240),
+          array(240, 0),
+          array(-5, 240),
+          array(240, -5),
+          array(-5, -5),
+          array(0, 0)
+        );
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getFrameRate
+     */
+    public function testGetFrameRate()
+    {
+        $this->assertEquals(25, $this->object->getFrameRate());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setFrameRate
+     */
+    public function testSetFrameRate()
+    {
+        $this->object->setFrameRate(12);
+        $this->assertEquals(12, $this->object->getFrameRate());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setFrameRate
+     * @dataProvider getWrongFrameRates
+     * @expectedException \InvalidArgumentException
+     */
+    public function testSetWrongFrameRates($framerate)
+    {
+        $this->object->setFrameRate($framerate);
+    }
+
+    /**
+     * Data provider for testWrongFrameRates
+     *
+     * @return array
+     */
+    public function getWrongFramerates()
+    {
+        return array(array(-5), array(0));
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getAudioCodec
+     */
+    public function testGetAudioCodec()
+    {
+        $this->assertEquals('audiocodec1', $this->object->getAudioCodec());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setAudioCodec
+     */
+    public function testSetAudioCodec()
+    {
+        $this->object->setAudioCodec('audiocodec2');
+        $this->assertEquals('audiocodec2', $this->object->getAudioCodec());
+        $this->object->setAudioCodec('audiocodec1');
+        $this->assertEquals('audiocodec1', $this->object->getAudioCodec());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setAudioCodec
+     * @expectedException \InvalidArgumentException
+     */
+    public function testSetWrongAudioCodec()
+    {
+        $this->object->setAudioCodec('audiocodec4');
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getAudioSampleRate
+     */
+    public function testGetAudioSampleRate()
+    {
+        $this->assertEquals(44100, $this->object->getAudioSampleRate());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setAudioSampleRate
+     */
+    public function testSetAudioSampleRate()
+    {
+        $this->object->setAudioSampleRate(22050);
+        $this->assertEquals(22050, $this->object->getAudioSampleRate());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setAudioSampleRate
+     * @expectedException \InvalidArgumentException
+     * @dataProvider getWrongAudioSampleRate
+     */
+    public function testSetWrongAudioSampleRate($samplerate)
+    {
+        $this->object->setAudioSampleRate($samplerate);
+    }
+
+    public function getWrongAudioSampleRate()
+    {
+        return array(array(-5), array(0));
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getVideoCodec
+     */
+    public function testGetVideoCodec()
+    {
+        $this->assertEquals('videocodec2', $this->object->getVideoCodec());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setVideoCodec
+     */
+    public function testSetVideoCodec()
+    {
+        $this->object->setVideoCodec('videocodec2');
+        $this->assertEquals('videocodec2', $this->object->getVideoCodec());
+        $this->object->setVideoCodec('videocodec1');
+        $this->assertEquals('videocodec1', $this->object->getVideoCodec());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setVideoCodec
+     * @expectedException \InvalidArgumentException
+     */
+    public function testSetWrongVideoCodec()
+    {
+        $this->object->setVideoCodec('videocodec4');
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getKiloBitrate
+     */
+    public function testGetKiloBitrate()
+    {
+        $this->assertEquals(1000, $this->object->getKiloBitrate());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setKiloBitrate
+     */
+    public function testSetKiloBitrate()
+    {
+        $this->object->setKiloBitrate(500);
+        $this->assertEquals(500, $this->object->getKiloBitrate());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setKiloBitrate
+     * @dataProvider getWrongKiloBitrate
+     * @expectedException \InvalidArgumentException
+     */
+    public function testSetWrongKiloBitrate($kbrate)
+    {
+        $this->object->setKiloBitrate($kbrate);
+    }
+
+    public function getWrongKiloBitrate()
+    {
+        return array(array(-5), array(0));
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getGOPsize
+     */
+    public function testGetGOPsize()
+    {
+        $this->assertEquals(25, $this->object->getGOPsize());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setGOPsize
+     */
+    public function testSetGOPsize()
+    {
+        $this->object->setGOPsize(100);
+        $this->assertEquals(100, $this->object->getGOPsize());
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::setGOPsize
+     * @dataProvider getWrongGOPsize
+     * @expectedException \InvalidArgumentException
+     */
+    public function testSetWrongGOPSize($GOP)
+    {
+        $this->object->setGOPsize($GOP);
+    }
+
+    public function getWrongGOPsize()
+    {
+        return array(array(-5), array(0));
+    }
+
+    /**
+     * @covers FFMpeg\Format\DefaultFormat::getMultiple
+     */
+    public function testGetMultiple()
+    {
+        $this->assertEquals(320, $this->object->getMultiple(321, 16));
+        $this->assertEquals(320, $this->object->getMultiple(319, 16));
+        $this->assertEquals(320, $this->object->getMultiple(313, 16));
+        $this->assertEquals(304, $this->object->getMultiple(312, 16));
+        $this->assertEquals(336, $this->object->getMultiple(329, 16));
+        $this->assertEquals(16, $this->object->getMultiple(8, 16));
+    }
+
+}
+
+class DefaultFormatTester extends DefaultFormat
+{
+
+    protected $audioCodec = 'audiocodec1';
+    protected $videoCodec = 'videocodec2';
+
+    protected function getAvailableAudioCodecs()
+    {
+        return array('audiocodec1', 'audiocodec2', 'audiocodec3');
+    }
+
+    protected function getAvailableVideoCodecs()
+    {
+        return array('videocodec1', 'videocodec2');
+    }
+
+    public function getExtraParams()
+    {
+        return '-f format';
+    }
+
+    public function getMultiple($value, $multiple)
+    {
+        return parent::getMultiple($value, $multiple);
+    }
+
+}