If your asset lists "Not all platforms transcoded." as shown above, chances are that it has failed completely. Unfortunately the warning message in the inspector is a bit misleading. You can check if you still get an import error in the console by selecting the video asset and hitting RMB - Reimport.
Unfortunately Unity seems to be not too flexible when it comes to input video formats, as can be seen on this documentation page: https://docs.unity3d.com/2021.1/Documentation/Manual/VideoSources-FileCompatibility.html
Encoding for video file tracks must use a supported codec. Each platform supports specific codecs that can change with each version of the platform.
Video files that use unsupported codecs trigger an error message in the Editor and you must convert them to a compatible codec before you can use them.
H.264 is the optimal supported video codec for most platforms. It offers the best cross-platform compatibility, but the Linux Editor doesn’t support this codec.
For information about codec support, see the official platform documentation for your Editor. See the links below for codec compatibility for Windows and macOS:
Windows codec compatibility
macOS codec compatibility
Unfortunately both the Unity documentation page, as well as the linked Media Layer documentation page for MacOS is just listing container formats, but not bitstream essence formats supported in each container. :rolleyes: A .mov container allows many different encodings of the contained video stream.
On Windows support for additional codecs a while back could typically be installed via e.g. installing ffdshow filters (which were wrappers around ffmpeg), unfortunately I'm not really up to date about this topic on Windows, let alone what the respective workaround on MacOS would be. Strangely Unity seems not to be using the decoders installed on the machine, or fails to do so without error. Unfortunately this is an issue that would need to be asked on the official Unity forums, as it's a bit outside our expertise.
What we would recommend as a workaround for now, is to try to transcode the video files (the .mov files exported from Spine) to H.264, as this would be the best chance that it can be read and transcoded to all build-platforms by Unity. Unfortunately I can only provide recommendations for transcoding software that worked well in the past on Windows (several years ago these were XMedia Recode, Media Coder, or using ffmpeg directly). If anyone knows useful transcoder applications for MacOS, any input would be very much appreciated.
