当 VideoPlayer.renderMode 设置为 Video.VideoTarget.RenderTexture 时，要在其中绘制资源的 RenderTexture。
如果 RenderTexture 是 TextureDimension.Tex2D ，视频帧将直接绘制到此目标中。为了获得最佳性能，RenderTexture.width 和 RenderTexture.height 应该与视频媒体的相应属性完全匹配。
If the RenderTexture is of TextureDimension.Cube the video frames will be interpreted as a cubemap in one of the 4 supported layouts (horizontal or vertical orientation of a cross or strip layout) based on video aspect ratio. The cubemap faces of the video frame are drawn to the 6 faces of the RenderTexture. For a one-to-one pixel mapping, RenderTexture.width and RenderTexture.height should match the size of the individual faces contained within the video media's cubemap (eg. for a 2048x1536 horizontal cross cubemap video, the RenderTexture cube size should be set to 512x512).