-> I wanted a java/servlet function which extracts the mimeType of a file that we are putting for uploadAEM Assets already extracts Mimetype and persist under asset's metadata:/content/dam/test.jpg/jcr:content/metadata/dam:MIMEtypeIn Servlet, you could use the service as I have mentioned[0] to detec...

You can use Apache Sling - MIME Type Support (commons.mime and commons.contentdetection) in AEM.To access asset's mimetype, use the API Asset (Adobe CQ 5.6.1 Java Documentation 5.6.1 API)

Please help us with following:Are you using touch UI or classic one?Videos for which you don't see thumbnails, does it have some other auto generated thumbnails? If yes, share the same.

You should use following Assets API.https://docs.adobe.com/docs/en/aem/6-0/develop/ref/javadoc/com/day/cq/dam/api/Asset.html#getMetadata() Here is the sample: http://adobeaemclub.com/servlet-to-get-all-tags-assigned-to-a-dam-asset-in-json-format/

IIUC allowBulkEdit property is used in context of WCM (foundation page component) and not applicable for DAM metadata editor. Following metadata schema should be used to customise the metadata editor fields.https://docs.adobe.com/docs/en/aem/6-1/administer/content/assets/metadata-schemas.html

Yes it should work. Property dam:status is on metadata node, hencepath = /content/dam(/.*)/jcr:content/metadatanodeType = nt:unstructuredCondition: dam:status==approved (without quotes)