What is the AVS file format?
An .avs file is a plain-text script for AviSynth, a frameserver application for non-linear video processing on Windows. Rather than editing video files directly, an .avs script describes a processing pipeline: a source filter loads footage (for example, AviSource() or FFmpegSource2()), and subsequent filter calls handle resizing, color correction, deinterlacing, noise reduction, and more. The file contains no embedded video data.
AviSynth works by presenting a virtual AVI interface to the host application. When a tool such as VirtualDub2 or an x264 encoder opens an .avs file, it receives a synthesized video stream generated by the filter chain - as though it opened a real AVI file - without needing any knowledge of AviSynth itself. This makes .avs scripts a common preprocessing step in encoding workflows.
The scripting language supports variables, conditionals, and user-defined functions. Comments are prefixed with #. The companion .avsi format is an AviSynth include file containing reusable function libraries, typically placed in the plugins directory for automatic loading at startup.
AviSynth was created by Ben Rudiak-Gould in 2000. The actively maintained fork, AviSynth+, adds 64-bit support and high bit-depth processing (8-bit to 32-bit float). The modern cross-platform alternative is VapourSynth, which uses a Python-based scripting model. Both AviSynth and AviSynth+ remain Windows-only.
Security & safety
RISK: MEDIUMAn AVS script is plain text, but AviSynth scripts can call external functions and load plugin DLLs via LoadPlugin(). A malicious .avs from an untrusted source could attempt to load a harmful DLL or execute a script that stresses resources. From trusted encoding communities, AVS files are safe to use.
Format details
in a nutshell- Stardent AVS X Image - Raster bitmap format from Stardent's Application Visualization System (AVS) software, early 1990s. Entirely obsolete; no modern software supports it.
- AVS Video Editor project / sequence file - Some versions of AVS Video Editor (Online Media Technologies) saved project sequences with .avs extension.
Programs that open AVS files
Windows5 apps
AviSynth+ (runtime)
Open-source Install AviSynth+ runtime, then load the .avs in VirtualDub2 or pass it to an encoder (x264/x265/FFmpeg). AviSynth itself is the script interpreter, not a standalone player.
Avisynth (original)
Open-source Install the AviSynth 2.6 runtime; open the .avs in VirtualDub or a compatible encoder. Note: AviSynth+ is the recommended modern choice.
VirtualDub2
Open-source File > Open Video > select .avs; VirtualDub2 calls AviSynth to render the script and displays the video. Requires AviSynth+ installed.
Notepad++ (script editing)
Open-source Open the .avs file as plain text to read or edit the script. Syntax-highlighting add-ons for AviSynth exist. Technical details
deep spec| Format type | Plain-text scripting language defining a video processing pipeline (frameserver) |
| Text encoding | ASCII; UTF-8 supported for file paths in AviSynth+ r2768+ |
| Typical file size | 100 bytes - 50 KB (script text only; referenced video files are external) |
| Frameserver model | Exposes a virtual AVI interface - host applications receive a synthesized video stream from the filter chain |
| Script structure | Sequential filter chain: source filter → processing filters → optional output; supports variables, conditionals, user-defined functions |
| Comment syntax | Lines beginning with `#` are comments |
| AviSynth+ additions | 64-bit support, high bit-depth processing (8-bit to 32-bit float), new filter APIs beyond original AviSynth |
| Include files | `.avsi` files are AviSynth function libraries; placed in the plugins directory they are auto-loaded at startup |
| Platform | Windows only; AviSynth+ adds partial cross-platform support but remains predominantly Windows |
| Host application compatibility | Works with any AVI-capable application: VirtualDub2, x264/x265 encoders, MeGUI, FFmpeg (via avsr plugin) |
| Modern alternative | VapourSynth (`.vpy`) - cross-platform, Python-based video scripting with a comparable filter-chain model |
| Released | 2000 (AviSynth 1.0 by Ben Rudiak-Gould) |
| Latest version | AviSynth+ 3.7.x (active fork, ongoing) |
| Specification | avisynth.nl |
AVS conversions
Community Q&A
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