Updating Materials to 4.18
If your pre-4.18 project uses Media Textures inside a Material, you may need to update your Material and change the Sampler Type to the new External type.
Materials still use a Texture Sampler and Media Texture, however, the Texture Sampler must be set to External.
Media Textures implement a new texture API called External Textures that on some platforms, provides a more optimal way of video playback.
For example on Windows, the video frame data is decoded from the file before being copied to the CPU memory buffer.
Once in the CPU memory buffer, it is then uploaded to the GPU into a
UTexture where the Texture is sampled within a Material.
Some decoders can bypass this transfer of data and have the ability to decode video on the GPU directly.
For example, on Android and iOS devices the video decoders will decode the compressed video on the GPU so the video frames are already on the GPU allowing for much more efficient video playback.