How to parse the aspect-mode option

[Productionstudioffm]

How does one parse the aspect mode option of omxplayer? I tried a lot of different options, but did not succeed.

Using the following two variants in '/etc/systemd/system/omxplayersync.service' for example didn't work:

ExecStart=/usr/bin/omxplayer-sync -a stretch -muvb /home/pi/video.mp4 ExecStart=/usr/bin/omxplayer-sync --aspect=stretch -muvb /home/pi/video.mp4

When I send this to the regular omxplayer, it works: omxplayer -o hdmi --aspect-mode stretch /home/pi/video.mp4