With setting the padding values to Zero (0) – the padding-top is then:

/*** to quick css - better to place with the concerning page ID ***/

.mfp-iframe-holder {
  padding: 0px !important; 
}

.mfp-iframe-holder .mfp-content {
  height: 90vh !important;  /*** the wanted height ***/
  width: 50.625vh;  /*** the calculated width is then ***/
}


.mfp-iframe-scaler {
  padding-top: 178%;  /*** 100 x 16 / 9 = 177.88 ***/
}

for an alb that had these aspect-ratio input fields – it would be nice to have another one (for wanted height)  if the lightbox case is choosen.

the aspect-ratio is determing the padding-top value. And the wanted height determins the width value:

Calculation on having aspect-ratio of the video and a wanted height.

.mfp-iframe-holder {
  padding: 0px !important; 
}

.mfp-iframe-holder .mfp-content {
  height: (videoHeight)vh !important;
  width: (rValue x videoHeight)vh;
}

/*** 100 x Aspect Ratio = rValue ***/
.mfp-iframe-scaler {
  padding-top: rValue%;
}

for example on choosing 85vh height for a 9/16  lightbox video:

.mfp-iframe-holder {
  padding: 0px !important; 
}

.mfp-iframe-holder .mfp-content {
  height: 85vh !important;
  width: 47.81vh;
}

.mfp-iframe-scaler {
  padding-top: 178%;
}

Custom-Class to lightbox mainClass

das video alb oben hat jetzt die custom-class: video-portrait

damit könnte man nun für alle 9/16 portrait videos zumindest die css Einstellungen setzen.

Änderung in video.php:

if( ( false !== stripos( $src, 'youtube.com/watch' ) ) || ( false !== stripos( $src, 'vimeo.com/' ) ) )
{
	$element_styling->add_classes( 'container', 'avia-video-external-service' );

	$src .= ( strpos( $src, '?' ) === false ) ? '?autoplay=1' : '&autoplay=1';
	$output_html = "<a href='{$src}' class='mfp-iframe lightbox-link' data-custom_class='{$custom_class}'></a>";
}
else if( ! empty( $src ) )
{
	$element_styling->add_classes( 'container', 'avia-video-standard-html' );

	$output_html = "<a href='{$src}' rel='lightbox' class='mfp-iframe lightbox-link' data-custom_class='{$custom_class}'></a>";
}

Änderung in avia-snippet-lightbox.js:

beforeOpen: function()
{
	//add custom css class for different styling
	if( this.st.el && this.st.el.data('fixed-content') )
	{
		this.fixedContentPos = true;
	}

	if( this.st.el && this.st.el.data('custom_class') )
	{
		var elementCustomClass = this.st.el.attr('data-custom_class');
		this.st.mainClass = this.st.mainClass + ' ' + elementCustomClass;
	}
},