WebM is the format browsers record in. Online voice recorders, screen recording extensions, meeting tools and many web apps that capture your microphone save their output as WebM, usually with Opus audio inside, and some video downloads arrive as WebM as well. Few desktop players, phones or audio editors handle it gracefully, and transcription and podcast services often reject it. This page opens with MP3 as the output; drop the WebM files and convert, and you get just the audio as an MP3. Any video track in the file is discarded. For a voice recording or a meeting, 128 kbps is plenty; for music pulled from a video, 192 kbps is a good default and there is no point going far above the bitrate of the source. Larger WebM videos take longer, since the whole file has to be read in your browser, and files up to 200 MB are supported. Everything runs locally using FFmpeg compiled to WebAssembly, so recordings of calls and meetings stay on your device. For MP4 or MOV videos use MP4 to MP3 Converter, and to get a written transcript of the recording use Speech to Text Audio Transcriber.
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.