Well that issue might be a "cousin" to this issue, but unfortunately the information is not on point.
If JRiver could do the following then the problem could be solved:
1) Enable a video file to be executed either in pause mode or to go immediately into pause mode when executed.
2)Then a push of the pause/play toggle would pull it into playing mode when the time was right which, depending on the file, could be anywhere from one to five seconds.
I can do this manually either using the keyboard or the screen on my iphone with the JRiver remote; however, I have to be quick and paying more attention than I'm always able to.
Alternately, maybe JRiver could have a setting where the user can decide to start videos in pause mode and then have the program switch to play mode after an assigned amount of time, like 2 second or 5 seconds or a nice array from 1 second to maybe 8 seconds.
The point is the the big 1920 x 1280 or even UHD files play fine once the buffer catches up, but it takes a while to get into that position and while that's happening I'm watching a black screen and listening to the video's soundtrack.