Upload M4R file from your device memory or cloud or via URL
Once uploading is complete, press the convert button
Wait until the end of the conversion and download new OPUS file
M4A is an audio file compressed using MPEG-4 technology, which has a lossy compression algorithm. The M4R file contains the ringtone in the M4A MPEG-4 file format, which uses the default audio format to store the song in the iPhone. The M4R format, like M4A, is designed to download audio to Apple devices through iTunes. Such a file can be created by converting other formats or uploading it from the official iTunes store. You don't have to look for converters or special programs, you can make m4r from m4a using standard tools of any operating system by changing the last letter of the extension manually. But for this to work like an iPhone ringtone, remember that it can only be created from songs purchased from the iTunes music store.
OPUS file is an audio file created in the Opus format, a lossy audio format designed for streaming on the Internet. It uses both SILK (used by Skype) and CELT (from Xiph.Org) codecs and supports variable bit rates from 6 kbps to 510 kbps. Opus is a completely open source, royalty-free, highly versatile audio codec. Opus is good for streaming both speech and music over the Internet. The Opus codec is used for Voice over IP (VoIP), video conferencing, in-game chat. The Opus format is supported by various software, including the TeamSpeak VoIP application, the Mozilla Firefox browser, the GStreamer framework, and the VLC media player. The main advantages of OPUS are the high audio quality and good compression achieved through dynamic adaptive streaming.