interactive mode has been recently enabled by default.
It will be much better if key guide like below is shown when gst-play starts or a key is pressed (here 'k' key)

interactive mode - key guide
k             : key guide
space         : pause
Q(q) or ESC   : quit
>             : play next
<             : play previous
+             : increase playback rate
-             : decrease playback rate
d             : change playback direction
t             : trick mode
left          : seek forward
right         : seek backward
up            : volume up
down          : volume down

Otherwise, we (esp. for newcomer) have to look into the source which key has which functionality.

Please review this.