The result of this command is undefined. Some players will play backward to x, some will play forward to the end of the disc, and some will search to x. This is because the XCMDs cannot know that x is less than the current frame
(they do not query the player for the current frame #), so they issue a play forward with a stopping point that's earlier. Different players respond to this condition differently. Therefore, this operation is officially undefined as far as the XCMDs go. You can, however, use "playvideo videoFrame(),x", which will always work properly.