No, they are two different applications. MPlayer is a multimedia player developed initially for linux and then ported to other OS. It's very good, it plays almost every everything, and it has for instance a lot of filters and so on. But most users may find it hard to use it.
Fortunately MPlayer can work together with another application (the video window can be embedded in the other application GUI, it obeys commands sent by the application). So SMPlayer is just a front-end which uses MPlayer to actually play the videos.
SMPlayer is the window you see, the menus, the preferences dialog... (along with other things you don't see, like functions to control MPlayer). But SMPlayer knows nothing about playing files. It doesn't even know what a codec is. MPlayer on the other hand, opens the files, decodes them, displays the video and plays the audio. Subtitles are also read, parsed and displayed on screen by MPlayer.
Currently MPlayer doesn't support DVD menus... Well, in fact it does if compiled with dvdnav support. The last time I tested it, it didn't work quite well. Anyway, even there are no DVD menus, you can still select your desired title, chapter, audio track, subtitles... in the SMPlayer menus.
MPlayer has several output drivers, for video and sound. SMPlayer allows you to select the one you want among all of them (Preferences -> General).
For video it's recommended that you use xv (linux) or directx (windows). They use hardware acceleration and give the best performance. The inconvenience about directx for Windows Vista users is that it disables Aero.
x11 and directx:noaccel are drivers without hardware acceleration. They give the worst performance. Moreover directx:noaccel gives a bad quality in fullscreen mode.
gl and gl2 will use 3D acceleration from the graphic card. They will give better performance than directx:noaccel and x11 but no so much as directx or xv. gl/gl2 can be useful for Windows Vista users.
For sound, you should usually use oss or alsa in linux. I don't like esd or arts, they use to use more CPU.
In windows the sound drivers are dsound and win32. I read that dsound can cause sometimes audio-video sync problems. If you notice that problem try win32 instead.
Other drivers allows you to save the video as image files or write the sound to the disk. These drivers are not officially supported by SMPlayer. Use them only if you know what you're doing.
It seems to be a problem with the NVidia cards or their drivers on Windows. gl/gl2 does work when using the real MPlayer window, but not when the video is embedded in another application. There's no known fix. The only thing you can do is either use directx instead of gl/gl2 or check the option to use the MPlayer window in Preferences -> Advanced.
Update: this problem has finally been fixed in MPlayer r25972.
You didn't choose a folder for storing the screenshots. Do it in Preferences -> General, and the screenshot option will be enabled.
With some formats (ike mp4 or ogm), MPlayer can't change the audio track at runtime. By unchecking the option "Fast audio track switching" you'll be able to change the audio in those formats.
Preferences -> Keyboard and mouse. You'll be able to change most key shortcuts.
SMPlayer is being developed by using Qt, which is a C++ library that allows cross-platform development. The same source code can be compiled on Windows, Linux and Mac OS. More info: http://trolltech.com/products/qt
MPlayer can player most common formats "out of the box". But for codecs that haven't been yet implemented natively, it's necessary to install a package with binary codecs. You can get it from the MPlayer download page.
On Windows, install the codecs in the mplayer/codecs subdirectory. On linux distros the package may be available as a regular package, maybe with the name of w32codecs or something like that.
If the option "Show icon in system tray" (in menu Options) is not checked, then yes, the two options do the same: quit the application.
But if that option is enabled, then Open -> Close will just hide the application (and stop the current file), but SMPlayer is still running. Open -> Quit really quits the application, no matter if the system tray icon is enabled or not.
Support for audio CDs was added in version 0.5.18.
Under Windows it's not possible to play audio CDs yet.
Not implemented yet.
Probably MPlayer couldn't play the file. Open the mplayer log (Options -> View logs -> MPlayer), you'll probably find an error message in the latest lines.
On Windows is quite common that some MPlayer builds fail because they have been compiled with no support for some feature that SMPlayer tries to use. The error message could give you a clue. If it complains about cache, try disabling the cache in Preferences -> Performance. If it complains about fontconfig try to use a ttf font instead of a system font.
The video equalizer was easy to do because MPlayer has slave commands to change brightness, contrast and so on at runtime. But I'm afraid it doesn't have similar commands for audio, so this can't be done.
That would be nice, but TV support is not planned for now. Currently I don't have a TV card, so I can't implement it.
Some options require to stop the MPlayer process and start it again with new parameters. That's why playing interrupts for a moment.
SMPlayer crashed, but MPlayer is still running. Kill the MPlayer process in the task manager.
Anyway if SMPlayer crashes, it's a serious bug that should be fixed. Report it.
Probably your MPlayer is translated into another language. SMPlayer looks for some English texts in the output of MPlayer. In this case it looks for "Exiting... (End of file)". As MPlayer displays the messages in another language SMPlayer fails and won't work properly. Unfortunately the language of MPlayer can't be changed without recompiling it. But recents versions of SMPlayer allow to change the messages that it should look for (Preferences -> Advanced -> MPlayer language).
SMPlayer can work with MPlayer 1.0rc1 (it hasn't been tested with older releases). Anyway that version is very old and it's not recommended at all. A lot of new things and improvements have been added since then. For instance changing audio in avi files or seeking in flv or ogm files don't work with that version.
You should use at least MPlayer 1.0rc2, although some new interesting features have been added after its release. I recommend to use at least MPlayer SVN r25843 (from 2008-01-23).
In the MPlayer download page you can get a svn tar.bz2 ready to compile. And compiling it is very easy (in linux, I mean...)
Video filters -> Add black borders
Currently the only way is to add a video filter like expand=:::::4/3 in Preferences -> Advanced -> Options for MPlayer.
When you use directx as video driver (Preferences -> General) the video can only be displayed on one monitor. If you use instead directx:noaccel, gl or gl2 the video will be displayed in any monitor (users of nvidia cards, please read this).
Anyway if you prefer to use directx is still possible but you have to add the -adapter option in Preferences -> Advanced -> Options for MPlayer (Options field). -adapter 1 will display the video on the 1st monitor, -adapter 2 will display it on the 2nd monitor, and so on (I think).
Check the option Change volume just before playing in Preferences -> General -> Audio.
This option requires a MPlayer build which is patched to add a new option (-volume) for it. The build included in the package for Windows has this patch applied. The patch can be found here.
This happens when you're using directx as video driver (Preferences -> General). You can change it to gl or gl2 (users of nvidia cards, please read this).
SMPlayer uses two ini files: smplayer.ini and smplayer_files.ini. Both are stored by default in $HOME/.smplayer (Linux) or C:\Documents and Settings\your_username\.smplayer (Windows XP).
You can also see it in the SMPlayer log (Options -> View logs), look for a line like this:
* ini path: '/home/ricardo/.smplayer'smplayer.ini stores the SMPlayer configuration while smplayer_files.ini stores the settings of the files you have played.