To edit and change aspects of any Strip, you can use the same

shortcuts applied in 3D modeling tasks. The most used shortcut to

manipulate Strips is the G key. Select any Strip and press the G key to

move it back and forward in time.

At the borders of the strip, you also find a vertical marker at the

beginning and end. You can click to select those markers and using the

G key contract or expand the Strip.

If you enabled the transparent option for rendering PNG files as an

image sequence, you would be able to compose it with a background

easily. Since each channel works as a layer, Strips at the bottom always

appear in the back of a composition. Placing a still image at the bottom

of your stack makes it appear in the back (Figure 8.17).

Figure 8.17 - Image in the back

To ensure you can see a composition using transparent PNG

sequences, make sure you have the Alpha Over option at your

Sequencer's Sidebar. By default, a Strip starts with the Alpha Over

enabled. Only with that option active, you see transparency applied to

Strips (Figure 8.18).