MP4 to SLN Converter

Extract Asterisk PBX audio from MP4 in SLN format

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Asterisk PBX Native

SLN is the standard audio format for Asterisk systems. Converting MP4 audio to SLN creates prompts your PBX can load directly.

Prompt Library Builder

Batch convert MP4 videos to SLN and build your complete IVR prompt library in one session — efficient PBX content creation.

Cloud Processing

No Asterisk installation needed for the conversion. Our servers extract and format the SLN audio from your MP4.

How to convert MP4 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

MP4 (MPEG-4 Part 14) is the most widely used multimedia container format in the world, standardized by the Moving Picture Experts Group as part of the MPEG-4 specification in 2003. Built on the ISO base media file format (MPEG-4 Part 12), which itself drew from the Apple QuickTime container, MP4 uses a hierarchical atom/box structure that can encapsulate virtually any type of media data. The container most commonly packages H.264 or H.265 video with AAC audio, though it also supports a wide range of alternative codecs including AV1, VP9, MPEG-4 Visual, AC-3, and ALAC. The design supports advanced features such as streaming hints for progressive download and adaptive streaming, chapter markers, multiple audio and subtitle tracks, metadata tags, and embedded thumbnail images. A standardized structure and broad codec support have made MP4 the default choice for online video platforms, mobile devices, digital cameras, and operating system media libraries. HTML5 video with H.264 in MP4 is supported by every major web browser, establishing the combination as the universal baseline for web video delivery. Efficient packaging overhead, combined with the compression capabilities of modern codecs it carries, enables high-quality video distribution at practical file sizes across bandwidth-constrained networks and storage-limited devices.
Initial release: 2003
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 MP4 to SLN?

SLN is Asterisk PBX's native audio format for IVR prompts, voicemail greetings, and hold music. Converting creates audio your PBX system can use directly.

What uses SLN files?

Asterisk, FreePBX, and other Asterisk-based PBX systems load SLN files natively for voice prompts and automated responses.

What sample rate should I use?

Standard Asterisk uses 8000 Hz (sln) for narrowband and 16000 Hz (sln16) for wideband. Choose based on your PBX configuration.

Can I batch convert?

Upload several MP4 files and create multiple SLN voice prompts at once — build your entire PBX prompt library in a single session.

Is SLN raw audio?

Yes — SLN is headerless signed 16-bit linear PCM. Asterisk knows the format based on the file extension and configured sample rate.

Does SLN strip video?

Yes — only the audio track from your MP4 is kept. The result is a raw signed linear audio file for PBX use.

MP4 to SLN Quality Rating

4.6 (12 votes)
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