You can use button setup... to turn your container field into a button.
In button setup, you can specify Go To Related Record (GTRR) as the singe script step performed when the button is clicked.
With the GTRR step selected, click specify and make the choices you need so that the step looks something like this:
Go To Related Record [Show Only Related Records ; From table: "//put your portal's table name here" ; Using Layout: "//Put the name of your portal table's layout"]
This will switch you to the other layout with just the record matching the portal row you clicked so that you can use this layout to display the video in a larger format.
Note: this is a "safe" use of GTRR. For warnings on the dangers of GTRR in other uses, check the filemaker help system in Filemaker 11 or click the link to the following thread:
Perfect!! Thankyou very much