A KAR file is a Standard MIDI File with the song lyrics embedded and time-synced to the melody, so a karaoke player can show the words while the music plays. On Windows, open it with the free Van Basco's Karaoke Player to get synchronized lyrics; VLC plays the music but will not display the words. To convert to MP3, render it through MuseScore or TiMidity++ with a soundfont.
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Identify a fileA .kar file, also known as the Karaoke MIDI file, is similar to the traditional .mid file used in various MIDI applications and players. Unlike the description sometimes given, a .kar file does not hold reference locations to external audio tracks - it IS a Standard MIDI File, containing a sequence of timed note events that a synthesizer turns into sound. What distinguishes it is an additional track that embeds the song lyrics in text format, time-synchronized to the melody for word-by-word display during playback.
The metadata stored in a .kar file typically includes the song title, the artist or album name, and other related details - conventionally placed in @T, @A, and @I header lines at the start of the first MTrk track chunk. Lyrics themselves are carried as FF 01 text meta-events (the Soft Karaoke @-tag format, with a @KMIDI KARAOKE FILE identifier) or as FF 05 lyric meta-events.
Because .kar stores a musical score rather than sampled audio, the same file can sound different depending on the synthesizer or sound bank used. Files are remarkably compact - a complete karaoke song with full lyrics typically weighs between 5 KB and 150 KB. Since .kar shares the MThd magic bytes with any MIDI file, renaming .kar to .mid usually allows any MIDI player to open it; the music plays correctly, but the synchronized lyrics will not be displayed.
A .kar is passive MIDI event data with no embedded code or macros, so the format itself is low-risk. Historic note: a 2012 Windows MIDI parsing flaw (CVE-2012-0003) allowed code execution via a crafted MIDI in Windows Media Player - long since patched, so keep your OS and players updated. The main practical 'risk' is disappointment: a .kar may sound thin because playback depends on the device's soundfont, and a non-karaoke player won't show the lyrics at all.
Windows4 apps
VLC media player
Open-source Plays the music via a MIDI synth (set a SoundFont in Preferences > Input/Codecs > MIDI). Plays the song but does not display karaoke lyrics. 
MuseScore
Open-source File > Open the .kar to view it as notation, edit it, and export the audio to MP3/WAV. 
Van Basco's Karaoke Player
Free Open the .kar to play the music and show synchronized scrolling lyrics - the classic free MIDI-karaoke player.
Karafun Player
Freemium Modern karaoke app; open the .kar (or its catalogue) to play with on-screen lyrics. Free player with paid song library. macOS3 apps
VLC media player
Open-source Open the .kar to play the music with a configured soundfont (no lyric display). 
Apple Logic Pro
Paid Import the MIDI to assign software instruments and produce/render audio (lyrics are not used as karaoke). Linux2 apps
TiMidity++
Open-source Play from the terminal with on-screen lyric display: 'timidity song.kar' renders the MIDI and prints synced lyrics. Android1 app
VLC media player for Android
Open-source Open the .kar to play it (uses a soundfont synth; no karaoke lyric display). | File structure | Standard MIDI File (SMF) - one `MThd` header chunk followed by one or more `MTrk` track chunks |
| Magic bytes | `4D 54 68 64` (ASCII `MThd`) at byte offset 0, identical to a `.mid` file; no `.kar`-specific file signature exists |
| Lyric embedding | Lyrics stored as `FF 01` text meta-events (Soft Karaoke `@`-tag style, with `@KMIDI KARAOKE FILE` identifier) or `FF 05` lyric meta-events, time-aligned to the melody track |
| MIDI format variant | SMF Format 0 (single track) or Format 1 (multi-track); the lyric/header track is typically the first `MTrk` chunk in Format 1 files |
| Byte order | Big-endian - all multi-byte integers follow the MIDI specification's big-endian convention |
| Data encoding | Binary; delta-time timestamps use variable-length quantity (VLQ) encoding, 1-4 bytes per event timestamp |
| Compression | None - variable-length delta-times keep event data compact without a separate compression layer |
| Typical file size | 5 KB - 150 KB; a full karaoke song with synchronized lyrics is usually well under 100 KB |
| MIME type | `audio/midi`; also used as `audio/x-midi` and `application/x-midi` |
| Timing resolution | Defined by the `division` field in the `MThd` header (ticks per quarter-note); tempo set dynamically via `FF 51` meta-events in µs/quarter-note |
| Score vs. recording | Stores note and control events, not sampled audio - a synthesizer or sound bank renders playback; the same file can sound different on different hardware or software |
| Header metadata convention | First track conventionally starts with `@KMIDI KARAOKE FILE`, followed by `@V` (version), `@I` (info), `@L` (language), `@T` (title), and `@A` (author) text events |
| Platform support | Windows, macOS, Linux, Android, iOS, and hardware arranger keyboards and karaoke machines |
| Interoperability | Renaming `.kar` to `.mid` allows any standard MIDI player to open the file; music plays correctly but synchronized lyrics are not shown |
| Legacy status | Largely superseded for home use by CD+G disc karaoke, MP4 video karaoke, and streaming karaoke services; `.kar` files persist in legacy collections and on arranger keyboards |
| Released | Mid-1990s (the .kar lyric convention popularised by Tune 1000 / the MIDIOKE scene) |
| Latest version | No separate spec - based on Standard MIDI File 1.0 (1988); lyrics carried in text/lyric meta-events |
| Open standard | Yes · royalty-free |
| Specification | midi.org |
