Track Transparency
You can use Track Transparency mode to set the transparency for the entire track, or to precisely control the transparency across individual clips in the Timeline. Setting the transparency for clips in Track Transparency mode is an alternative to setting the Opacity for the clips in the Editor panel. Track Transparency can be used to create a superimposed effect or to create a fade in and fade out effect.
Note: When you use the Track Transparency slider in the track head, the transparency setting for the track affects all clips on the track and sets the baseline for any keyframe-based Opacity/Transparency settings for individual clips. For example if the Track Transparency slider is set to 50%, this will be used as the maximum opacity value for any clips on the track. This means a clip keyframe setting of 100% Opacity will present as 50% opacity when the clip is added to that track.
You can create a superimposed effect or fade with Track Transparency
To use Track Transparency mode1 In the Edit workspace, select a track in the Timeline, and on the Timeline toolbar, click the Track Transparency button 
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.2 In the Timeline, do one of the following
• To adjust the transparency for the entire track, in the track head area, drag the Track Transparency slider to set the value you want or type a value in the box at the end of the slider.
• To vary the transparency, on a clip, click the yellow transparency line to add as many keyframe nodes as you need. Drag the nodes down to increase transparency.
If you want to delete keyframes, right-click a keyframe node and choose the corresponding command.
3 Click the Track Transparency button to exit Track Transparency mode.