Liferay as a product and platform is very customizable. One particular area of customization is media icons--icons that are displayed in search results for documents and media of various sorts, such as items linked to pages, etc. By default there is a specific configuration of icons and supported media types. These can be overridden and extended.
In Control Panel->Server Administration -> Portal Properties, the default settings for the dl.file.icons portal property can be seen. This can be overridden in portal-ext.properties to add additional media types.
For example, add the line below to the portal-ext.properties file so Liferay recognizes the .mp4 format. This specification of the 'dl.file.icons' overrides the default portal.properties setting.
Additionally, the images used by Liferay for a given media type can be overwritten. Image files named to match a recognized media type (such as mp4.png) can be placed in the <liferay base folder>/webapps/ROOT/html/icons folder and Liferay will pick them up and use them after a restart.
Alternatively, overrwritten images can also be placed in the webapp/images folder of a custom theme and deployed as a war file.
Additionally, custom images --in png format-- can be substituted for existing images that Liferay uses for various features, their function implied by the file name ---such as 'journal.png', 'sitemap.png', or 'message_boards.png' these would placed in the icons folder as described above.
Simple customizations such as custom media icons and supported media types are an effective away to customize and personalize a Liferay installation to meet a desired look for a particular installation.