WebM to SLN Converter

Extract WebM audio as Asterisk PBX signed linear online

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Web Video to VoIP

Extract WebM audio and encode it as SLN — ready for use as hold music, prompts, and announcements on Asterisk phone systems.

Server-Based Work

All processing runs remotely. No Asterisk CLI tools or WebM decoders needed on your machine — just a browser and your file.

Fast Results

Audio extraction and SLN encoding are fast. Most WebM files produce a download-ready SLN telephony file in under a minute.

How to convert WEBM to SLN

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose sln or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your sln file right afterwards

About formats

WebM is an open, royalty-free multimedia container format developed by Google and launched at the Google I/O conference in May 2010. The format pairs the Matroska container (a subset of MKV) with VP8 or VP9 video codecs and Vorbis or Opus audio codecs, creating a fully open media stack designed specifically for web use. Google released WebM alongside the VP8 codec under permissive BSD-style licensing, removing patent and royalty barriers that hindered the adoption of H.264 for open web video. The WebM container inherits the efficient binary structure of Matroska while restricting it to web-optimized profiles, ensuring fast parsing and lightweight implementation in browsers. WebM with VP9 achieves compression efficiency competitive with H.264 High Profile and approaching HEVC, making it practical for delivering high-quality video at reduced bandwidth. Major web browsers including Chrome, Firefox, Edge, and Opera support WebM playback natively, and YouTube uses VP9 in WebM as a primary delivery format for much of its content. The format supports features such as alpha channel transparency in video, making it valuable for compositing web graphics and overlays. More recently, WebM has been extended to support AV1 video, continuing its evolution as a vehicle for open codec adoption. The combination of competitive compression, zero licensing costs, and universal browser support makes WebM a cornerstone of royalty-free web multimedia delivery.
Developer: Google
Initial release: May 19, 2010
SLN (Signed Linear) is a headerless raw audio format storing 16-bit signed linear PCM samples at 8000 Hz mono, most closely associated with Asterisk) — the open-source PBX framework developed by Digium (now Sangoma Technologies). Within Asterisk, SLN serves as the native internal audio representation: every codec transcoding operation passes through signed linear as an intermediate step. This makes SLN the backbone of Asterisk's codec translation architecture. The format contains nothing but raw samples — no headers, no metadata, no framing — so parameters must be known in advance. While this lack of self-description might seem limiting, it is actually an advantage in telephony where sample format is fixed by convention and every overhead byte matters across thousands of simultaneous channels. The 8000 Hz rate aligns with the G.711 standard for traditional telephony, capturing the full 300-3400 Hz voice band. Asterisk also supports extended variants (sln16, sln32, sln48) for wideband audio. SLN files require no decoding — just direct memory mapping — making them ideal for real-time mixing, conferencing, and prompt playback in high-density VoIP environments.
Initial release: 1999

Frequently Asked Questions

Why convert WebM to SLN?

SLN is the raw audio format for Asterisk PBX. WebM web video audio can be extracted and used for VoIP prompts, hold music, or greetings.

What is SLN format?

SLN is 8kHz, 16-bit signed integer, little-endian raw PCM — the native telephony format for Asterisk open-source PBX platforms.

Does WebM Opus convert well?

WebM Opus or Vorbis audio is decoded and downsampled to 8kHz SLN. Speech content sounds clear on phone systems at this rate.

Can SLN be used elsewhere?

SLN is tailored for Asterisk PBX. While SOX can process it, the format mainly serves VoIP telephony environments.

Is the process fully automatic?

Yes — upload WebM, select SLN, download. Audio decoding, downsampling, and SLN encoding all happen on our servers automatically.