Opus to MP3
Convert an Opus file, the codec behind most voice notes and Discord recordings, to MP3 for software that cannot open it. Opus stays small at low bitrates that make MP3 audibly worse, so the MP3 usually ends up the larger file.
Opus to MP3 turns files from the format most voice notes and Discord clips use into MP3, for software that never added Opus support. Opus holds up at bitrates where MP3 already sounds noticeably worse, so the converted output often ends up the bigger of the two files. WebCodecs runs the decode, so a browser tab is needed.
Questions
Why would the MP3 end up bigger than the Opus?
Because Opus stays small at low bitrates where MP3 already sounds audibly worse, so matching Opus quality at a comparable bitrate often costs MP3 more bytes rather than fewer, the opposite of what converting usually does here.
What kind of source is this typically?
Voice notes and Discord recordings are the most common Opus files people convert, since Opus is the codec behind most of them and many players and devices still do not read it directly.
Which engine handles this, and where can it run?
mediabunny and WebCodecs decode the Opus audio, and mediabunny loads a LAME-based MP3 extension on demand as a separate chunk to encode the result at the chosen quality, low, medium or high. This is browser only; the command line and MCP refuse it and point to the web page.
What size should I expect?
Often close to or larger than the source Opus file, an unusual outcome among these pairs, since Opus already compresses efficiently at the bitrates it is typically used at.
What is the reverse page?
There is no dedicated mp3-to-opus page. Convert audio does not write raw Opus either, since Opus is not one of its output formats.