You can play the video after the upload action is done (through Add attachments). From the attachment section, you can click on the video attachment file to preview & play it. PFA the attachment with steps to do it OOTB in 8.3 version. It is similar to upload video using the attachments section and later click on it to play it in earlier versions.
If you are requirement is to play the video before the upload and later submit to the case, this is not present in the product. You need to have a custom attachments section to have a similar preview screen to play the video(using some player?) after upload and before submission to the case.