Recently, the time-manager-pugin seems to support video-export on Windows: https://github.com/anitagraser/TimeManager However, I can't find any instructions how to install this feature. I updated to time manger plugin, however, it still mentions "only Linux/OSX" - so how to install or activate this feature?
The pull request with the feature you mention has been merged (https://github.com/anitagraser/TimeManager/pull/295) but there hasn't been a new release of the plugin yet. Therefore, if you want to use this feature already, you need to download the plugin from Github (https://github.com/anitagraser/TimeManager/archive/master.zip) and install it manually (i.e. unpack the zip archive in the QGIS plugin folder).
Update 2019-06-09: I've released TimeManager 3.2.0 with video export on Win now!
The video export is a two-step process: first the image series is exported, then ffmpeg is started to create the video.
Concerning ffmpeg: The tool is available from https://ffmpeg.zeranoe.com/builds/
Unzip the ffmpeg archive, e.g. to
C:\Program Files\ and add the path to the bin library to your Windows Path environment variable:
Update 2019-10: The video export functionality has been removed in the last release due to issues on all platforms and lack of resources for fixing them.