M4V to SLN Converter

Extract M4V audio as Asterisk PBX signed linear online

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Apple Video to VoIP

Pull audio from M4V video and encode it as SLN — ready for hold music, prompts, and greetings on your Asterisk PBX platform.

Server-Side Encoding

M4V extraction and SLN encoding run on our servers. No Asterisk CLI tools needed — just your browser and an internet connection.

Private and Secure

M4V uploads are deleted after conversion. SLN output is removed within 24 hours — your telephony audio remains confidential.

How to convert M4V 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

M4V is a video container format developed by Apple Inc. and introduced alongside the iTunes Video Store in October 2005. Technically, M4V is nearly identical to the standard MP4 format (MPEG-4 Part 14), with the primary distinction being optional FairPlay DRM protection applied to purchased content from the iTunes Store. Unprotected M4V files are fully compatible with any player that handles MP4, as the underlying container structure and codec support are the same. The format typically contains H.264 video and AAC audio, supporting resolutions up to 4K and features like chapter markers, subtitle tracks, and metadata tags for title, artwork, and ratings. Apple chose the M4V extension to distinguish iTunes content from generic MP4 files, primarily so that DRM-protected purchases would be recognized by the Apple ecosystem of devices and software. M4V files play natively on macOS, iOS, iPadOS, and Apple TV, and unprotected versions work seamlessly in most major media players across all platforms. The format gained significant traction as the iTunes Store became a dominant platform for purchasing and renting digital movies and TV shows. Compatibility with the broader MP4 ecosystem means that video and audio streams within DRM-free M4V files can be processed by virtually any modern editing or transcoding tool without conversion.
Developer: Apple Inc.
Initial release: October 2005
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 M4V to SLN?

SLN is the raw audio format for Asterisk PBX systems. Converting M4V audio to SLN creates custom prompts and greetings from video.

What are SLN specifications?

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

Will M4V audio sound good on phones?

SLN at 8kHz provides standard telephone quality. Speech from M4V videos sounds clear — music may sound simplified at this bandwidth.

Do iTunes M4V files work?

DRM-protected iTunes purchases cannot be converted. Personal M4V recordings and unprotected downloads convert to SLN successfully.

Is the conversion automatic?

Fully automatic — upload M4V, select SLN, and download. Audio extraction, resampling, and encoding happen on our servers seamlessly.