The input texture must be readable such as WWW.texture.
I made this plugin for reducing GPU memory from WWW.texture.
1. Please move the directory 'Assets/TextureCompressor/Plugins' to 'Assets/Plugins'.
2. If your project supports ARMv7 only, remove 'Assets/Plugins/libETCPlugin.so' and rename 'libETCPluginARMv7.so' to 'libETCPlugin.so'. Otherwise, just remove 'libETCPluginARMv7.so'.