To embed a video in the Detailed text area:
(1) Click on the Add/Edit Details link to open the Details editor.
(2) Switch to the Html editor, using the < > button (in the bottom left hand corner of the Details editor – below the text entry box).
(3) Paste the video embed code into the text entry box.
(4) Change the width of the video to a value below 365 pixels – usually using a fraction like 4/5, 3/4, 2/3 to accomplish this – while keeping the height and width ratio the same (rounding up/down if appropriate).
(5) If necessary (though generally it isn't), iterate on (3) until you are happy with the result.
(Note: that sometimes the video embed code will include the height and width values twice, and, if so, it is advisable to adjust the values for both instances).