// create document
$factory = new \Sokil\Vast\Factory();
$document = $factory->create('4.1');

// insert Ad section
$ad1 = $document
    ->createInLineAdSection()
    ->setId('ad1')
    ->setAdSystem('Ad Server Name')
    ->setAdTitle('Ad Title')
    ->addImpression('http://ad.server.com/impression', 'imp1');

// create creative for ad section
$linearCreative = $ad1
    ->createLinearCreative()
    ->setDuration(128)
    ->setId('013d876d-14fc-49a2-aefd-744fce68365b')
    ->setAdId('pre')
    ->setVideoClicksClickThrough('http://entertainmentserver.com/landing')
    ->addVideoClicksClickTracking('http://ad.server.com/videoclicks/clicktracking')
    ->addVideoClicksCustomClick('http://ad.server.com/videoclicks/customclick')
    ->addTrackingEvent('start', 'http://ad.server.com/trackingevent/start')
    ->addTrackingEvent('pause', 'http://ad.server.com/trackingevent/stop');

// add closed caption file (Closed Caption support starts on VAST 4.1)
$linearCreative
    ->createClosedCaptionFile()
    ->setLanguage('en-US')
    ->setType('text/srt')
    ->setUrl('http://server.com/cc.srt');
    
// add 100x100 media file
$linearCreative
    ->createMediaFile()
    ->setProgressiveDelivery()
    ->setType('video/mp4')
    ->setHeight(100)
    ->setWidth(100)
    ->setBitrate(2500)
    ->setUrl('http://server.com/media1.mp4');

// add 200x200 media file
$linearCreative
    ->createMediaFile()
    ->setProgressiveDelivery()
    ->setType('video/mp4')
    ->setHeight(200)
    ->setWidth(200)
    ->setBitrate(2500)
    ->setUrl('http://server.com/media2.mp4');
    
// get dom document
$domDocument = $document->toDomDocument();

// get XML string
echo $document;

<?php

namespace Acme\Vast\ElementBuilder\Element;

use Sokil\Vast\Creative\InLine\Linear\MediaFile;

class AcmeMediaFile extends MediaFile
{
    public function setMinDuration($seconds)
    {
        $seconds = (int)$seconds;
        if ($seconds <= 0) {
            thow new \InvalidArgumentException('Invalid min duration specified, must be positive int')
        }
        
        $this->domElement->setAttribute('minDuration', $seconds);
        
        return $this;
    }
}

<?php

namespace Acme\Vast\ElementBuilder;

use Sokil\Vast\ElementBuilder;
use Acme\Vast\ElementBuilder\Element\AcmeMediaFile;

class AcmeElementBuilder extends ElementBuilder
{
    /**
     * <Ad><InLine><Creatives><Creative><Linear><MediaFile>
     *
     * @param \DOMElement $mediaFileDomElement
     *
     * @return AcmeMediaFile
     */
    public function createInLineAdLinearCreativeMediaFile(\DOMElement $mediaFileDomElement)
    {
        return new AcmeMediaFile($mediaFileDomElement);
    }
}

<?php

use Acme\Vast\ElementBuilder\AcmeElementBuilder;
use Sokil\Vast\Factory;

$elementBuilder = new AcmeElementBuilder();
$factory = new Factory($elementBuilder);

$document = $factory->create('4.1');

$ad = $document->createInLineAdSection();
$creative = $ad->createLinearCreative();
$mediaFile = $creative->createMediaFile();

$mediaFile->setMinDiration(10);