This format extension is one of the Speex Audio formats. It is an open-source codec developed by Xiph.Org. Used for creating voice messages and transmitting voice over packet-based networks with a low level of security. It is an audio file with recorded voice messages that are packaged in an OGG file. Only certain media players can open it.

WavPack: a free lossless audio codec

This format is completely open. WavPack allows for both lossy and lossless compression. After compression, there is created a small file that can be played separately. WavPack also contains a correction file, which allows you to restore the original version. Supported only by certain audio players. This format has high sampling frequencies (192 kHz) and can be multi-channel (up to 255). It is easily converted to the mp3 format.