fpng for VapourSynth

This is a small plugin which allows fpng to be used with VapourSynth.

The motivation for this plugin was to dump frames of a VapourSynth script to PNGs faster than was possible with imwri.

Usage

Plugin Documentation

Usage is similar to imwri.Write() with ImageMagick options replaced with fpng options.

.. function:: Write(clip clip, string filename[, int firstnum=0, int compression=1, bint overwrite=False, clip alpha])
   :module: fpng

   Write will write each frame to disk as it's requested. If a frame is never requested it's also never written to disk.

   Parameters:
      clip
         Input clip. Only RGB24 is supported.

      filename
         The filename string must have one or more frame number substitutions. The syntax is printf style. For example "image%06d.png" or "/images/%d.png" is common usage.

      firstnum
         The first image number in the sequence to write.

      compression
         Matches fpng flags which are:
         0 - fast compression
         1 - slow compression (smaller output file)
         2 - uncompressed

      overwrite
         Overwrite already existing files. This option also disables the requirement that output filenames contain a number.

      alpha
         A grayscale clip containing the alpha channel for the image to write. Apart from being grayscale, its properties must be identical to the main *clip*.

Example Python Script

The examples/dump_frames.py script included in this repository is not necessary to use the plugin, but may be useful either to directly dump frames or as a reference for the plugin usage.

usage: dump_frames.py [-h] -o OUTPUT [--filename FILENAME] [--overwrite] script

Dump frames from VapourSynth script. Script will be converted to RGB24 using frame properties if they're available.

positional arguments:
  script                The VapourSynth script to fetch frames from

optional arguments:
  -h, --help            show this help message and exit
  -o OUTPUT, --output OUTPUT
                        The output directory for dumped images (default: None)
  --filename FILENAME   The filename template for dumped images (output is always .png) (default: frame_%d)
  --overwrite           Set to overwrite existing files (default: False)

Building

The author isn't overly familiar with C++ "build systems" so details may be missing. Broadly the only dependency not included with the source should be the VapourSynth SDK. The build system tested is MSYS2's mingw-w64 on Windows 10. It is quite likely that building is possible on other systems given sufficent experience building C++ libraries using those other systems.

meson setup -Dstatic=true build
cd build/
ninja

# If all goes well libfpng.dll should exist within the build directory

Bundled Dependencies

Some dependencies are directly copied into the src/ directory from their respective projects. It is the author's understanding that this usage is compatible with the applicable licenses.

From fpng fetched 2022-04-30

• fpng.h
• fpng.cpp

From libp2p fetched 2022-04-30

• p2p.h
• p2p_api.h
• p2p_api.cpp
• v210.cpp

From vs-imwri fetched 2022-04-30

• vsutf16.h
• Several methods within plugin.cpp also directly come from imwri.cpp