M4R to OPUS
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| File extension | .m4r |
|---|---|
| File category | Audio |
| Stands for | MPEG-4 PART 14 for iPhone ringtones |
| Developer | Apple Inc. |
| Overview | M4R is one of the extensions of MPEG-4 Part-14 and it is specially designed by Apple for iPhone ringtones. It is just the relabelling of AAC and M4A. This extension provides an excellent quality of ringtones for iPhones and the size of the ringtone is also small. There are certain steps that one needs to follow for the conversion of any song into this format (iPhone ringtone). Firstly, select any song of 30 seconds and covert it to AAC format using iTunes. Then rename this file using .m4r extension. Finally, by using the iTunes transfer your ringtone file to iPhone. This can be done by connecting your iPhone to the computer and syncing the playlist. Now a user can easily use this ringtone for phone ring, alerts, alarms etc. It should be noted that these files will be supported only by the latest version. Hence, use the current version of iTunes. |
| Technical description | It uses a lossy compression algorithm to encode the ringtones that is same as AAC and MP3 eareensions. But it has the additional feature of auditory masking which means it neglects other sounds which can be detected or recognized while listening or hearing another sound. It only discards the information which is surplus for the human ear. This results in good quality of iPhone ringtones. It takes less storage space without affecting the quality of audio. It is also a segment of MPEG-4 standard and this is stated in the ISO-IEC standard 14495-3. |
| Links | wikipedia.org (opens in new tab - official documentation) |
| File extension | .opus |
|---|---|
| File category | Audio |
| Stands for | Ogg OPUS |
| Developer | Xiph.Org |
| Overview | It is a format for audio files which compresses the audios using lossy compression. It neglects the redundant information which can not be processed by the human ear. Internet Engineering Task Force (IETF) has standardized this format. It has superseded the Vorgis and Speex. It offers low latency i.e. there is a less delay in the signal when it enters the system and when it emerges out, this results in real-time interactive communication like video conferencing. Due to its good audio quality, it is widely used by in various listening tests. |
| Technical description | OPUS has good compatibility with low-end embedded processors as it is less complex. Ranging from 6kbps to 510kbps, it can support both variable and constant bitrate coding. Also, the frame size from 2.5ms to 60ms is supported by this codec. It works smoothly and maintains stability (by avoiding the distortion) while mixing of packets from distinct streams. Speech, Hybrid and pure-CELT are the three different methods used for encoding the audios of varied frequencies. For compressing the Speech up to 8kHz, SILk is used which is an audio compression developed by Skype Limited. The next mode, Hybrid uses CELT to compress the audio files above 8kHz frequency or for wider bandwidth and frame sizes 10ms and 20ms are supported by this mode. CELT(Constrained Energy Lapped Transform) is an open and free audio compression format which is especially used in communication that requires low latency. For general audio, the last mode pure-CELT is used. CELT is used for frame sizes which are less than 10ms. |
| Links | wikipedia.org (opens in new tab - official documentation) |
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