The image is displayed without problems due to the acceleration being available on the first head but some of the frames get displayed on the second head in the same resolution so that the video can be seen there, too, albeit only in a flickering way. This way, of course, it is not possible to use the display on the second head because it is constantly disrupted. BTW (another bug), this video driver makes the mouse pointer disappear on both heads in fullscreen mode, even the option "-nograbpointer" does not change that.
Dear submitter, as the package mplayer has just been removed from the Debian archive unstable we hereby close the associated bug reports. We are sorry that we couldn't deal with your issue properly. For details on the removal, please see https://bugs.debian.org/732159 The version of this package that was in Debian prior to this removal can still be found using http://snapshot.debian.org/. This message was generated automatically; if you believe that there is a problem with it please contact the archive administrators by mailing ftpmaster@ftp-master.debian.org. Debian distribution maintenance software pp. Ansgar Burchardt (the ftpmaster behind the curtain)