To playback Hap5 videos with an alpha channel, the HAP Media plugin and possibly the WMF Media Player plugin for Unreal Engine 4 are required. Some other additional things to note:

• It appears the width must be evenly divisible by 32. Crashes can occur otherwise.
• It appears aspect ratio is not important.
• If video imports into unreal and opens but looks corrupted, it could be a video size issue. Trying using a different video size.

Unreal Media Player

This is what the Unreal Media Player asset settings should like like.)

Player: WmfMedia
Stream 0:
Type: Video
Format 0:
Codec: 48617035-767a-494d-b478f29d25dc9037 (Hap5)
Frame Rate: 30 fps
Frame Rate Range: 30 – 30 fps
Dimensions: 1920 x 1080
Video decoded on GPU

After Effects

(This is what the After Effects encoding settings should like like.)

Format: AfterCodecs .mov
Post-Render Action: None
Video Output:
Channels: RGB + Alpha
Depth: Millions of Colors+
Color: Premultiplied (Matted)
Format Options:
Hap Squish
WAV PCM
AfterCodecs v1.10.0
Video Codec: Hap / Hap Alpha
Algorithm: Vidvox / Squish Accelerated [Slow – HQ]
Compression: Enable Snappy Compression
Chunks: 1
VR Meta: None
Streaming: No Fast Start

Format Options:
Hap Squish
WAV PCM
AfterCodecs v1.10.0
Video Codec: Hap / Hap Alpha
Algorithm: Vidvox / Squish Accelerated [Slow – HQ]
Compression: Enable Snappy Compression
Chunks: 1
VR Meta: None
Streaming: No Fast Start