DirectShow Video Mixing Renderer (VMR-7) filter exhibits a (regression?) bug in Windows 10 systems. When aspect ratio preservation is enabled in VMR_ARMODE_LETTER_BOX
mode, which makes overall sense as default mode quote so often, the letterboxing does not work as expected.
The problem is easy to reproduce with a well known DShowPlayer
SDK sample application, with an edit enforcing VMR-7 mode. Once video is started, just resize the window and the parts not covered by video will not be erased as expected.
![](https://alax.info/blog/wp-content/uploads/2019/03/Clipbrd1-1-800x475.png)
Apparently this worked well earlier.