What is the LSX file format?
.lsx is a Windows Media metafile that acts as a streaming media redirector - a small text file that tells Windows Media Player where to find an actual audio or video stream on the internet. It is closely related to .asx and shares the same internal <ASX> (Advanced Stream indeX) XML-like syntax.
When a browser requests a URL ending in .lsx from a web server, the server returns an <ASX> payload that Windows Media Player intercepts and uses to open the referenced stream. Each <ENTRY> element contains a <REF> child whose HREF attribute points to the actual media location using mms:// or http:// URLs. Optional metadata elements - <TITLE>, <AUTHOR>, <COPYRIGHT>, and <DURATION> - are commonly included.
The internal structure is identical to .asx; the .lsx extension was specifically used for HTTP-redirected launch scenarios. The companion formats .wax (audio WMA streams) and .wvx (WMV video streams) share the same XML grammar and ASX version 3.0 root element.
.lsx files are plain text and can be opened in any text editor such as Notepad. The mms:// protocol they rely on was deprecated around 2013, and modern streaming uses .m3u8 (HLS) or direct HTTPS delivery instead. Windows Media Player (classic) was removed from Windows 11, making these files largely obsolete today.
Security & safety
RISK: LOWLSX files are plain text with no executable code. They can contain URLs pointing to arbitrary streams - opening an unknown LSX could connect to a malicious server and reveal your IP, but cannot directly execute code. Treat like any URL from an untrusted source.
Format details
in a nutshell- Lotus Symphony LSX extension file - Older IBM Lotus Symphony used .lsx for add-in extension descriptors - an entirely different binary/XML format.
Programs that open LSX files
Windows3 apps
Windows Media Player
Built-in Double-click the .lsx file; WMP launches and attempts to connect to the referenced stream. Note: mms:// streams no longer work; only active http/https streams will play. 
VLC media player
Open-source Rename .lsx to .asx, then Media → Open File in VLC. VLC reads ASX playlists and will attempt to connect to the stream URL. 
Notepad / any text editor
Built-in Right-click → Open with → Notepad to read the stream URL(s) inside. 
macOS1 app
VLC media player
Open-source Rename .lsx to .asx, open in VLC. VLC will attempt to connect to the referenced stream. 
Linux1 app
Technical details
deep spec| Format type | Text (XML/SGML-like metafile) |
| Root element | `<ASX>` element with version attribute (typically 3.0) |
| Stream reference | `<REF>` element with `HREF` attribute; value is `mms://` or `http://` stream URL |
| File encoding | ANSI (Windows-1252) or UTF-8; optional UTF-8 BOM |
| Typical file size | 200 bytes - 10 KB |
| Supported metadata elements | `<TITLE>`, `<AUTHOR>`, `<COPYRIGHT>`, `<BANNER>`, `<DURATION>` |
| Associated streaming protocol | `mms://` (Microsoft Media Server; deprecated ~2013) |
| Primary application | Windows Media Player 6.x and later |
| Related format variants | `.wax` (WMA audio redirect), `.wvx` (WMV video redirect), `.asx` (generic metafile) |
| MIME type | `video/x-ms-wvx` |
| Operating system | Windows (Internet Explorer / WMP integration required) |
| Current status | Legacy/obsolete - `mms://` protocol deprecated ~2013; Windows Media Player (classic) removed from Windows 11 |
| Released | late 1990s, with Windows Media Player 6.x |
| Latest version | N/A - superseded by modern streaming; no versioned updates |
| Specification | learn.microsoft.com |
LSX conversions
Community Q&A
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