Re-play-er is a free multimedia application available on the iPhone platform. Developed by Naoki Ide, this app allows users to easily replay specific parts of songs or videos to aid in learning a song, language, dance, and more.

With Re-play-er, users can play iTunes content, videos from their Camera Roll, and even YouTube content. Additionally, files created on a computer can be played on iTunes and then synced to the iPhone for playback.

The app supports a wide range of file formats including .aif, .aiff, .caf, .mp3, .aac, .m4a, .mp4, .wav, .mov, .mpv, and .3gp. However, it's important to note that depending on the compression format, some files may not be playable.

Re-play-er also offers useful features such as memo display, reverse playback, and speed control. These functions can greatly assist in the learning process. It's worth mentioning that the speed control function cannot be used while playing YouTube content.

Please note that Re-play-er requires iOS 10.0 or later to function properly. Additionally, DRM files are not supported, and iTunes files that are not downloaded to the iPhone cannot be played.

Overall, Re-play-er is a convenient and versatile app for iPhone users who want to easily replay specific parts of songs, videos, or other multimedia content for learning purposes.