The sources have been moved. You can find them here:

• smplayer: https://github.com/smplayer-dev/smplayer
• smplayer-themes: https://github.com/smplayer-dev/smplayer-themes
• smplayer-skins: https://github.com/smplayer-dev/smplayer-skins
• smtube: https://github.com/smplayer-dev/smtube