Sony HANDYCAM DCR-SX21 Operating Manual page 27

Using a DVD writer, etc., other than DVDirect Express
1
Connect a DVD writer, etc.,
to the  (USB) jack of your
camcorder with the USB cable
(supplied).
2
Select the recording media
that contains the images on
the camcorder screen.
[ USB CONNECT]: Internal hard disk
(DCR-SR21)
[ USB CONNECT]: Memory card
3
Record images on the
connected device.
4
Select [END]  [YES] after the
operation is completed.
Notes
Refer also to the instruction manuals supplied with devices to be connected.

Sony DVD writer may not be available in some countries/regions.
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US