range and extra frames. Issue here is that the movie backend would unconditionally use the start frame of the scene instead of the preview frame. Solved by passing an explicit "preview" argument. Strictly speaking, the preview argument is part of the renderdata struct, that is also passed to the code, but when rendering the final result we want to unconditionally render the full range regardless of the preview setting of the render structure. However, OpenGL rendering does use the preview range so we need to account for that when making those exports. This is also a nice chance to correct the filenames, which still used the full range.