To rename a custom field, open the data entry window, right-click the data field and choose Rename Field from the popup menu. You can also rename fields from the 'Database Setup' window (Tools=>Database Setup).
The Video table contains the following custom fields:
Text
Custom 01, Custom 02, Custom 03, Custom 04, Custom 19, Custom 20
Lookup
Custom 05, Custom 06, Custom 07, Custom 08, Custom 21
Multivalue lookup
Custom 31
Memo
Custom 30
Date
Custom 09, Custom 23
Numeric
Custom 10, Custom 22
Checkbox
Custom 11, Custom 12, Custom 13, Custom 14, Custom 15, Custom 16, Custom 17, Custom 18, Custom 24, Custom 25, Custom 26, Custom 27, Custom 28, Custom 29