I want to make a clip like the 24 TV drama, but i do not know how to make a clock? can anyone tell me how to do that?

How you do this almost entirely depend on what s/w you have available.

You could maybe use the new timecode feature of Premiere Pro2. i.e. ignore (or mask out) the frame count part just leaving a clock type display and changing the font if that optiuon is available.

or, and maybe better, because the clock display in 24 only shows three or four seconds at a time, just fraw three or four frames in Photoshop and get the timing right.

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