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WebPDecoderJN

Decode static or animated WebP images into individual frames (and metadata), using JNA and native libraries based on the libwebp library.

Includes native libraries for (must fit the JRE it is run with):

  • Windows x86, x86-64
  • Linux x86-64
  • Mac x86-64, arm64

Requirements

You need the WebPDecoderJN-*.jar file as well as JNA.

The -all variant contains JNA already, however if you are already using JNA in your project you should probably choose the regular variant to avoid conflicts.

Usage

You can use WebPDecoder.init() to extract the native libs for the platform from the JAR. This needs to be run once before any decoding attempts. If it is not used JNA will take care of looking for the library, which may still end up with extracting it from the JAR if it is not found in the system. Using init() just ensures that it is loaded from the JAR.

The WebPDecoder.test() function can be used to attempt decoding a WebP file contained in the JAR in order to test if the native libraries work properly.

Decode images using the WebPDecoder.decode(byte[] data) function and get a WebPImage object containing some metadata and the individual frames.

If your goal is to display the image in Swing this is outside the scope of this project, however this may give you a starting point. From what I understand you need an ImageProducer that provides the frames and then turn that into an Image object.

Javadocs

Test App

The test app can be run to try out if the loading of the native libraries and the decoding works. If you are not running it headless you can enter your own URLs and paths to image files and then view the individual frames and some metadata.

The native library is extracted from the JAR, unless it is found in the same directory as the JAR that contains the WebPDecoder class.

Optionally parameters can be provided:

java -jar WebPDecoderJN-TestApp-1.2-all.jar [URL] [decodeCount]
  • The URL will be filled as default value into the GUI.
  • If a decodeCount greater than 0 is provided, the URL will also be decoded that many times (before the GUI opens), which can act as a simple performance test, even in headless mode.

Compiling the Java library

Run gradlew build (personally I use something like gradlew -Dorg.gradle.java.home="C:/Program Files (x86)/Java/jdk1.8.0_201" build --console=verbose for specifying a specific JDK and verbose output). This creates various JAR files under lib/build/libs and test-app/build/libs. The -all variants include all dependencies.

Compiling the native libraries

Some libraries are already included in compiled form, although you may want to compile them yourself (or compile it for additional platforms).

The libraries are based on the WebP project. To decode animated WebP images normally both the libwebp and libwebpdemux dynamic libraries would be required. However for this project the required functions are built into a single dynamic library libwebp_animdecoder using the provided C "program" (really just a file for the linker to include the required code/exported functions).

See the build-native folder for platform-specific documentation. If you want to build for a new platform, you may need to adjust the instructions to fit your needs.

WebP library project license: BSD 3-Clause

The native library can then be put in lib/src/main/resources/ in a subfolder so that JNA can find it in the JAR (refer to JNA for the folder names).