It's very easy. Just open a video, and then select the option "Find subtitles on opensubtitles.org" within the Subtitles menu. A new window will show a list of suitable subtitles for the video you're playing. Select one and click on the Download button. The subtitle file will be downloaded and displayed in the video.
With some cards or video drivers the hardware video equalizer may not work. Go to Preferences -> General -> Video and enable the software equalizer.
Go to the Drive section in preferences and check the option "Enable DVD menus (Experimental)" and set your DVD drive.
Go to the SMPlayer preferences, select the Interface section, then select the "Skinnable GUI". Now you can choose among several skins. In linux you need to install the package smplayer-skins.
The easiest way to find the configuration files of SMPlayer is by selecting the option "Open configuration folder" in the Help menu. If you want to delete the current configuration and start with the default settings, just delete the file smplayer.ini (important: be sure SMPlayer is not running when you delete the file).
They are two different applications that work together. SMPlayer actually is not a media player... MPlayer is. MPlayer is a command-line application, it doesn't have menus or buttons. It is controlled by the keyboard. As this is not very user friendly, several graphical interfaces have been developed, and SMPlayer is one of them. So MPlayer is the playback engine, SMPlayer adds the buttons, menus, dialogs, and so on. The Windows packages already include a MPlayer build along with SMPlayer.
View -> OSD -> Subtitles only.
Disable the option 'Draw video using slices' in Preferences => General => Video
Multithreaded decoding requires a recent build of MPlayer or FFmpeg-mt in Linux. MPlayer2 automatically uses all cores, but MPlayer requires manual adjustment. You can adjust the number of threads used for decoding in Preferences -> Performance. Set it to equal or less than the number of cores (and threads in the case of hyperthreaded Intel CPUs) your processor has. Setting it to greater than your CPU is capable of will have no effect.
Select the option "Add black borders" in the video filters menu.
You can play YouTube videos at 1080p or even at 4K resolution with SMPlayer. You only need to make a small change in the SMPlayer configuration. In Preferences -> Network select mpv + youtube-dl in the option Support for video sites. Also be sure mpv is selected as multimedia engine in Preferences -> General.
This modification also makes the YouTube subtitles available in SMPlayer.
Note: Linux users must install youtube-dl.
This happens when using directx as video driver (Preferences -> General -> Video). You can change it to gl, gl2 or direct3d.
Some options require to stop the MPlayer process and launch it again with new parameters. That's why playback interrupts for a moment.