WEBM is a media file format designed for web use. It is based on the VP8 video codec and the Vorbis audio codec, making it highly efficient for video streaming on the web. WEBM supports high-quality video and is supported by most modern browsers, offering an open-source alternative to proprietary formats like MP4.
MP3 is an audio format that can compress and encode an audio file. It uses the lossy compression algorithm to contain audio data. The lossy compression helps to reduce the data significantly without losing audio quality. MP3s are created using different bit rates maintaining the original quality.