Hi everyone,
Our team recently spent some time troubleshooting why certain Apple ProRes (.mov) files refused to play in the Unreal Engine Media Player, despite having the “Apple ProRes Media” plugin enabled.
After some painful experiment on the frame rates / formats, we discovered that the Apple ProRes decoder in Unreal is strict about dimensions: The input resolution must be a multiple of 16.
If your video is, for example, 1440x1440 (2K), it will work fine (1440/16 = 90). However, if you are working with typical 1080p resolution (e.g., 1080x1080, 1080/16 = 67.5), the plugin may fail to decode the stream (The output log shows no errors but the video fails to play).
The Fix:
When exporting your source video from Premiere, After Effects, or Media Encoder, ensure your width and height are divisible by 16.
- Example: Change 1080px to 1024px or 1440px.
Once we adjusted the source files to hit these multiples, the Media Player recognized the ProRes files immediately. Hope this saves someone else a few hours of debugging 
Specs:
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Plugin: Apple ProRes Media
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Engine Version: 5.6.1