1. You need to set the stage of the
image size. We have taken the following image for the bar masking
effect.

2. Open flash and create a new file.
3. Import image to stage.
File > Import > Import to Stage
4. Fit the image on the stage using Align command
if you want to do this with precision. This goes as follows.
Modify > Align > Left
Modify > Align >Top
and then,
Modify > Document > Select Contents in
the Match
Insert frame on 60.
5. Rename the image layer to Image. Lock the image
layer.
6. Add one layer. Name it as Mask. Keep it selected.
7. Select rectangle tool and draw the rectangle with
no stroke over the image to cover it fully.
8. Right click on the rectangle and select Break Apart.
9. Using selection tool, make the slices of the rectangle
as shown below. No need to be precise for the dimensions of slices.

10. Once finished, select the sliced rectangle and
convert to symbol using F8. Select Graphics for option type and
name it as bar.
11. Select Mask layer. Insert Keyframe on 60th frame.
12. Select the first frame on the mask layer and shift
the rectangle to the top as shown below.

13. Keep the first frame selected on the mask layer
and change the Tween property to Motion.
14. Right click on the mask layer and Select Mask.
15. Export movie using File
> Export > Export Movie
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