OGG is an open container format, and the audio inside is usually Vorbis or Opus. You run into it in game files, Android notification sounds, open source software, Wikipedia audio clips and voice messages saved from Telegram. It sounds good for its size, but iPhones, many car stereos and some editing and presentation software still do not play it. This page opens with MP3 as the output, so you drop the OGG files and convert. OGG Vorbis is already lossy, so the MP3 is a second round of compression. Pick a bitrate at or above the original to avoid making it worse: most OGG music is between 128 and 256 kbps, and 192 kbps is a safe default. For voice messages, which are recorded at a very low bitrate, 128 kbps already keeps everything there is. The converter reads both Vorbis and Opus inside OGG, as well as files with the .oga extension. Each file converts in turn and shows its own status, so a damaged file is marked as failed without stopping the rest. Everything happens in your browser. For WhatsApp voice notes, which use the .opus extension, see Opus to MP3 Converter, and for uncompressed output choose WAV in the format buttons.
The split that matters most in audio formats is lossy against lossless. A lossless format such as WAV or FLAC stores enough information to reconstruct the original waveform exactly, which is why WAV files run around 10MB per minute of stereo CD quality audio. Lossy formats such as MP3, OGG Vorbis, AAC, and Opus use psychoacoustic models to discard sound that listeners are unlikely to perceive, typically hitting a tenth of the size for audio most people cannot distinguish in normal listening. The important consequence is that the discarded information is gone permanently. Converting MP3 to WAV inflates the file back to full size without recovering anything, and each further lossy conversion compounds the loss, an effect known as generation loss. The practical rule is to keep a lossless master and export lossy copies from it, rather than converting between lossy formats repeatedly. Bitrate is where quality and size are actually traded. At 128 kbps most listeners cannot reliably distinguish MP3 from the source on laptop speakers or earbuds, though the gap becomes audible on good headphones with dense music. At 256 to 320 kbps MP3 is effectively transparent for nearly everyone. OGG Vorbis reaches similar quality at a somewhat lower bitrate, because it is a newer design than MP3, and Opus does better still, which is why messaging apps and voice chat use it. Sample rate and bit depth apply to the uncompressed side. This tool writes WAV at 16 bit and 44.1 kHz, the CD standard, which is the format editing software and mastering workflows expect, and which every audio application on every platform can open without conversion.