VapourSynth source and filters plugin for working with digitized analog video and signals.

Decodes 4𝑓𝑠𝑐-sampled analog video signals to a digital video clip. The signal data must be orthogonal video system lines with well-formed blanking and syncing structure at a stable time base such as those from ld-decode and vhs-decode. These files normally have a .tbc extension indicating they are time-base-corrected and must have a metadata sidecar file in JSON or SQlite format.

For color decodes, this returns a clip (VideoNode) in VapourSynth’s YUV444PS format. For monochrome decodes, the clip is in VapourSynth’s GRAYS format. Behind the scenes, it employs ld-decode’s ld-chroma-decoder routines.

import vapoursynth as vs
from vapoursynth import core

clip = core.analog.decode_4fsc_video("/path/to/capture.tbc")

# The resulting YUV444PS format retains maximum quality from the decode, but
# the format is uncommon. Filters may not expect or work well with it. You’ll
# often want to convert it to something else using the built-in resize plugin
# or fmtconv.
# R′G′B′ for color/levels adjustment filters:
workable_clip = clip.resize.Point(format=vs.RGBS)
# For mvtools2 pipelines like QTGMC that require an integer format:
workable_clip = clip.resize.Point(format=vs.YUV444P16)
# Reducing chroma resolution closer to analog source aids some NR filters:
workable_clip = clip.resize.Spline36(format=vs.YUV422P16)

Y/C-separated signals such as from vhs-decode or S-Video capture are supported:

clip = core.analog.decode_4fsc_video("luma.tbc", "chroma.tbc")

Each source signal file must have a corresponding metadata sidecar file with the same base name and a .db or .json extension. If the metadata is in JSON format, a .db file will automatically be created in the same directory.

The decoder parameter accepts the same values as ld-chroma-decoder:

If not specified, the decoder is auto-selected based on the video system in the TBC metadata.

Setting dropout_correct=1 replaces signal dropout regions identified in the TBC metadata with data from nearby clean lines, based on the algorithm from ld-decode-tools’ ld-dropout-correct. Luma and chroma are sourced independently using FIR frequency separation to find the closest match for each.

For multi-source correction, pass additional TBC captures of the same content via dropout_composite_or_luma_extra_sources (and dropout_chroma_extra_sources for Y/C-separated formats). Sources are aligned using VBI frame numbers when available (laserdisc CAV/CLV), falling back to sequential frame alignment for sources without VBI data (e.g., VHS-decode output).

When dropout correction is enabled, the following frame properties are set:

• VapourSynth (>= R55)
• Qt6 (Core module)
• FFTW3
• SQLite3

macOS (Homebrew):

brew install qt6 fftw sqlite

Ubuntu/Debian:

sudo apt install libqt6core6 libfftw3-3 libsqlite3-0

Fedora:

sudo dnf install qt6-qtbase fftw-libs sqlite-libs

Arch Linux:

sudo pacman -S qt6-base fftw sqlite

Windows:

Install VapourSynth, then ensure Qt6, FFTW3, and SQLite3 DLLs are available in your PATH or alongside the plugin.

The simplest way to install is via pip into a Python environment such as a venv:

pip install vsanalog

This installs both the native plugin and a Python module with type-hinted wrappers like vsanalog.decode_4fsc_video. The plugin is automatically loaded when you use the Python module.

Alternatively, obtain or build the plugin for your operating system and place vsanalog.dll, vsanalog.dylib, or vsanalog.so into your VapourSynth plugins directory.

See BUILDING.md for build dependencies and instructions.

Signal decoding functionality comes from ld-decode-tools’ ld-chroma-decoder. This was done to take advantage of great work already done on that project including the composite video separation/transformation decode processes, which would have been hard to replicate.

Using ld-decode-tools’ code directly (in a submodule here) forces a few design decisions:

• To ease legal distribution of this plugin, I must make this project available under the GPL 3 license or one that’s compatible.
• ld-chroma-decoder’s code relies on QtCore and Qt’s SQLite plugin which would make them dependencies. I had a machine learning model write a pure SQLite alternative to the JSON to SQLite metadata sidecar converter. By avoiding Qt’s SQLite plugin, the plugin is less likely to cause crashes from a symbol collision with another linked Qt such as PyQt’s when using vspreview.

Machine learning (Claude Opus 4.5 model) was heavily leveraged in the early development of this plugin to reduce the tedium of gluing the various components together.

• jsaowji’s ldzeug2 is an excellent alternative VapourSynth video source for TBC files and provides neural network approaches to separating composited luma and chroma components—something that vapoursynth-analog doesn’t have. It moves more 4fsc processing to the Python domain for flexible scripting opportunities. It focuses on composite NTSC, ST 170, and Japan format signals.
• ld-decode-tools comes with an ld-chroma-decoder tool to decode TBC files to component R′G′B′ or Y′Cb′Cr′ stream output for use in command line workflows and an ld-dropout-correct tool for generating a pre-corrected intermediate based on upstream dropout detection.
• tbc-video-export is a convenient wrapper around ld-chroma-decoder and ffmpeg for producing digital video files from TBC files. It’s handy if you need to deliver a lossless interlaced intermediate to someone else for filtering or color grading.