Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window cosmosffmpeg-cosmosffmpeg_1.0.7_2021-1025-18166.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.
