Both files also work nicely on my ancient WinXP computer. The old MPC-HC 1.5.2.3456 neither has problems using the internal filters nor using the external LAV Filters 0.69.0.85. Tiny Player also plays both files using LAV Filters 0.69.0.85, it only gets the aspect ratio of the WebM file wrong (plays it with 4:3), but this is probably an issue of the player. MKVToolNix (latest stable version, but replacing the GUI with the old v. 10 GUI) also accepts both files. So I suppose that something must be broken at your end... Cheers manolito