Ok, that's good info, thanks.
If Omxplayer won't stream
Then make a named pipe (mkfifo) and stream to it, out of it. Use omxplayer instead. Assuming that omxplayer will play from a pipe.
mplayer http://path/to/file -dumpstream -dumpfile abc.fifo
cat abc.fifo | omxplayer -
Or use the standard output/input like a pipe.
youtube-dl http://blah/blah - | omxplayer -
Or use youtube-dl to get it, then play it with omxplayer.
This thread shows
Just how many ways that you can skin a cat with a Linux box, or board even,
Just how versatile Linux and open source software is,
Just how learning some basic Linux shell, command line, and basic shell scripting can make you functional across different platforms and devices,
If no software exists that does exactly what you want, then easily make your own with what is extant.