Source
File: wp-includes/widgets/class-wp-widget-media-video.php
public function render_control_template_scripts() {
parent::render_control_template_scripts()
?>
<script type="text/html" id="tmpl-wp-media-widget-video-preview">
<# if ( data.error && 'missing_attachment' === data.error ) { #>
<div class="notice notice-error notice-alt notice-missing-attachment">
<p><?php echo $this->l10n['missing_attachment']; ?></p>
</div>
<# } else if ( data.error && 'unsupported_file_type' === data.error ) { #>
<div class="notice notice-error notice-alt notice-missing-attachment">
<p><?php echo $this->l10n['unsupported_file_type']; ?></p>
</div>
<# } else if ( data.error ) { #>
<div class="notice notice-error notice-alt">
<p><?php _e( 'Unable to preview media due to an unknown error.' ); ?></p>
</div>
<# } else if ( data.is_oembed && data.model.poster ) { #>
<a href="{{ data.model.src }}" target="_blank" class="media-widget-video-link">
<img src="{{ data.model.poster }}" />
</a>
<# } else if ( data.is_oembed ) { #>
<a href="{{ data.model.src }}" target="_blank" class="media-widget-video-link no-poster">
<span class="dashicons dashicons-format-video"></span>
</a>
<# } else if ( data.model.src ) { #>
<?php wp_underscore_video_template(); ?>
<# } #>
</script>
<?php
}