SMPlayer Support Forum

I think mpv already supports this. Be sure you're using mpv as multimedia engine in preferences, general. If it still doesn't work you may also need to change the video output in preferences, general, video.

I checked my settings and I have mpv (General, Multimedia engine) and Default (Output driver), and it works perfectly with MP4 but not MKV. I tried the other two Output drivers gpu and direct3d, and they still work for MP4 only, though the gpu one has incorrect aspect ratio when it auto-rotated the MP4 video, it inherited the original aspect ratio thus it was stretched. Again, they worked for MP4 only and not MKV. Perhaps there is an option I could pass in the Advanced, MPlayer/mpv tab? Right now they are blank.

If this may help, I have:
SMPlayer 18.2.2 (rev. 8937), 64-bit, Portable Edition
Windows 7 64-bit
i5-4460 (no separate video card)

Thanks.

Maybe mpv doesn't support it yet in mkv videos.

Can you provide a link to a small sample video?