Make a key frame (or more than one at different points) on the Opacity control. You can get to it by selecting the layer and pressing T. Or open up all the triangles to find it. Set the opacity to zero to make the layer invisible.
I was a rusted on MPC (and more recently its derivatives MPC-HC and MPC-BE) fan until recently when the MPC devs flagged that it would not be continued. So I started looking to see what else was out there.
While the MPCs are still very capable players I've increasingly been using MPV, another mplayer-derived open-source project.
It has a fairly minimal UI ...
Potplayer plays the HQX HR file I generated using ffmpeg. You have to tell Potplayer to use ffmpeg's MP4/QT demuxer by setting Preferences -> Filter Control -> Source/Splitter -> MP4/QT to FFmpeg MP4 Source/Splitter.
With current technology no, you "can not"; and with more powerful technology it is a waste of resources.
You do not need to stream a gigapixel video, you need to stream a video, receive the new "interest" zone, process the coordinates and display a new version of the video. Even arrange different chunks of different videos.
This is what google maps, bing ...