Modern browsers include audio features that can decode and play common audio files. This makes it possible to build simple editing tools that run locally without a traditional upload-and-process server workflow.
When you choose a file, the browser reads it into memory and decodes the audio data. The waveform is drawn from the decoded samples, making it possible to show the loud and quiet parts visually.
Cutting audio in the browser usually means copying only the selected sample range into a new audio buffer. The tool can then encode that selected range into a downloadable format such as WAV or MP3.
This workflow is privacy-friendly because the file can be processed on your device. However, it also means performance depends on your browser, CPU, memory, and the size of the audio file.
For very large files or professional editing features, a server-side encoder such as FFmpeg may be more reliable. For simple cuts, browser-based editing is convenient and fast enough for many everyday tasks.