Transitions are used between clips. iMovie adds transitions between every video clip by default, but you can modify them to change visual effects.
Tap the icon in the timeline for the transition you want to change. Then choose a transition from the inspector at the bottom of the screen and tap on it.
None No effects
Theme Custom effects from the chosen theme
Cross-dissolve One clip dissolves into the next
Slide Choose a direction for each clip to slide into the next
Wipe Choose a direction for each clip to wipe into the next
Fade Choose a white or black fade from one clip to the next
You can also adjust the duration of each transition up to 2 seconds long by tapping on a duration on the inspector.
Add Video Clips with iMovie
Each transition style has its own sound effect. Turn it on or off by tapping the mute icon on the inspector.
Fade In and Out
Fading in from black at the beginning of the movie or fading out to black at the end gives it a professional look.
Tap the Project Settings button and then tap to turn the fade options on or off.
Adding a Title
Tap the clip in the timeline to reveal the inspector.
Tap the Title button.
Tap to select a style.
Tap Center or Lower to change where it appears on the screen.
Resources: Other Video Editing Apps
VidLab (Mac and PC)
This multi-track, multi-clip video editor allows you to add text, artwork, music, video, sound effects and more to your videos. Animate text over your videos with the included collection of fonts or install custom fonts from your own collection. Import music from iTunes and record your own audio for narration and sound design.
StopMotion Studio (All devices)
Free professional grade video editing app for iOS features to edit and produce Ultra HD and Full HD videos easily and save in full resolution (4k, 1080p, and 720p). The app includes 40 music and sound samples. The Magic Eraser removes unwanted parts of the image.
Replay (iPhone and iPad)
Select up to 200 clips or photos per project and explore 30 editing styles. Choose from built-in music to pair tracks with your video. You can even edit the pace. The app adds blurred background behind portraits and square photos to replace black bars. Note: It doesn’t support 4K.
Pinnacle Studio (All devices)
Make movies with multi-layer animations, transitions, and titles. It includes a dedicated audio mixer. Export projects from the iOS app to Pinnacle Studio on the PC to continue editing where you left off.
Clips Video Editor (iPhone)
With an uncomplicated interface, this app makes it simple to add music, dissolve transitions, add text slides and more. Mix audio and record voiceovers. You can edit in HD video. Play with slow motion or fast motion too.