You need to specify the absolute or relative path to the executable. For example, assuming that you put the abplayer file in your home directory, in the xterm you type:

Or, if you are at the same folder than the executable, you can use the simpler relative path: ./abplayer

Alternatively, you can put the executable at user scripts folder, named for example /home/user/bin, and add this folder to the PATH variable, by writting the following lines in your /home/user/.profile file:

This way, next time you open xterm, you can simply write "abplayer" without need to specify any path (and this will be also true for any future script you put in your bin folder).