MediaPlayer

MediaPlayer is the default player for all audio and video files. Thanks to its ffmpeg backend, a plethora of widely used formats are supported. Its simple interface has all the controls you'd expect:

The slider of the progress bar allows you to quickly skim to a position, resting the mouse over it shows the current and remaining time of the clip. Clicking on the time display to the right of it, toggles between length, current and remaining time.
Below that you find the usual controls to skip to the previous track, play/pause, stop and jump to the next track. Then comes a volume control (clicking the speaker symbol toggles muting) and a VU meter.

Audio and video playback

Since there aren't any specific features for audio playback, we'll go straight to video or general features.

Available to all media is the File info… (ALT I). It shows information about the currently loaded file, like playing time or details of the audio/video track and its codec.

Most of the often used commands from the menus are also available from a right-click context menu on the video area. Convenient when in full-screen mode.
Under Video you'll find options to zoom the window to various levels or force the aspect ratio to some standard values. Leaving the aspect ration to the default Stream settings should work best for correctly encoded files.

MediaPlayer supports subtitles in SRT format. To have them show up under Subtitles, their filenames have to be identical to their video file, with a suffixed language name and ".srt" instead of the video's extension. For example:

MyMovie.avi
MyMovie.Deutsch.srt
MyMovie.English.srt
MyMovie.Français.srt

Multiple audio tracks, most often used for several languages inside one video file, are available from the Audio track submenu. The Video | Track submenu offers the same when having multiple video streams available.

You can toggle the Full screen mode (ALT ENTER or F or a double left-click), hide MediaPlayer's window borders and controls with Hide interface (ALT H or a double right-click) or have its window Always on top (ALT A).

Playlists

MediaPlayer | Playlist… (ALT P) opens a window with the files currently queued up for playback. Double-clicking an entry starts playing it.

You can add more files by dropping them into the list and rearrange their position via drag & drop. New files are added in the order they were selected from a Tracker window. Drag & dropping them with the right mouse button shows a context menu to insert them sorted (alphabetically).
From the Edit menu you can Randomize or Remove (DEL) an entry from the list or delete the actual file with Move to Trash (ALT T).

Of course, you can Save a playlist and later Open it again, or start it with simply double-clicking the playlist file.

Rating

Here you can set a Rating of the current clip between 1 and 10, or choose Reset rating to set it back to "unrated" (= "0").

In Tracker, ratings are displayed in a "Rating" attribute column as a number of stars. Five stars represent the 10 possible values, resulting in half-star steps. For example, a rating of 7 is shown as 7 / 2 = 3.5 stars: ★★★⯪☆.
You can edit the rating directly in Tracker as well: Select the file, choose Edit name from the File menu and press TAB to get into the "Rating" column. Now you can enter the new numerical value which will turn into a star rating after hitting ENTER.

Settings

There are several settings to fine-tune MediaPlayer's behavior:

The first batch, Play mode, is pretty self-explaining.
Start playback automatically, close windows when finished or play clips in a loop.
From the pop-up menu you choose MediaPlayer's launch behavior. Should it resume playing where it left off last time: always, never, or ask every time.

Next are different View options.
You can opt to Use hardware overlay if available, which cuts down CPU usage but only works for one video window and needs a supporting video card driver.
You can Scale movies smoothly (when not in overlay mode) which uses very fast filtering to smooth over otherwise blocky pixels when zooming video or watching in full-screen mode.
Scale controls in full-screen mode if you prefer slightly bigger controls, maybe because you watch the screen from a bit farther away when in full-screen mode.
Then there are settings for Subtitle size and Subtitle placement. They can be shown at the Bottom of video, which will always have them overlayed over the picture. Or Bottom of screen, which allows you to resize the window vertically and have the subtitles appear in the black bar at the bottom instead.

The last setting determines the volume of clips whose windows are not currently active. You can have them all blaring at Full volume, at less confusing Low volume or quietly Muted.

Keyboard controls

MediaPlayer offers convenient key combinations to control playback without using the mouse.

These keys are assigned to the functions of the control buttons. They are always the bottom left letter keys on the keyboard, i.e. they are used independently of your current keymapping. The above keys correspond to a standard US-american keymap.