Hello Will,
In our documentation we try to warn users about using the Media Player as it is still considered an experimental feature at this time. There have been certain compatibility issues in regards to certain encoded media formats, specifically H.264 and .MP4 file types.
As a reference, here is a link to our Documentation page on this feature. To that note, we are well aware of the issues that are occurring with this feature, which is why we urge users not to include this as a major piece of their projects for the time being.
Media Framework Functionality
Please keep in mind that hotfixes are typically for major crashes and bugs that are affecting large numbers of users. All bugs that were addressed within a hotfix are listed on the hotfix release notes. If you do not see a fix for specific bugs there, it is probably not going to be within that hotfix and either may be in a later hotfix or a later release build.
As a note, I would like to add I have a tutorial I have updated to be compatible for 4.9.1 that you might fight helpful.
Media Player Tutorial
Thank you for taking the time to write up your report, and let me know if you have further comments or questions.
Cheers,