Add your MMF file
Drop one or more .mmf files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
MMF to OPUS
Re-encoding .mmf audio as .opus changes how the sound is compressed and which players will accept it. Free, private, and validated — the file never leaves your browser.
100% private for supported formats
Runs on your deviceConvert supported files
Drop MMF files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting SMAF mobile audio to Opus audio
Re-encoding .mmf audio as .opus changes how the sound is compressed and which players will accept it. An .mmf file is a Yamaha SMAF (Synthetic music Mobile Application Format) file, the ringtone format of early-2000s mobile phones. Rather than a recording, an .mmf usually contains sequenced music that a phone's Yamaha synthesizer chip performed live, sometimes blended with short PCM samples.
An .opus file contains audio compressed with the Opus codec, stored in an Ogg container. Opus represents the current state of the art in lossy audio, beating MP3, AAC, and Vorbis in listening tests at nearly every bitrate from whisper-thin speech settings up to transparent music encoding. For this route the practical draw is best-in-class efficiency at essentially every bitrate and royalty-free with an open reference implementation — balanced against older car stereos, AV receivers, and MP3 players have never heard of it, which is worth knowing before you commit a large batch.
Why convert MMF to OPUS?
The practical trigger for this conversion is usually a mismatch: with .mmf, no current phone, browser, or OS plays it at all. Switching to .opus buys you best-in-class efficiency at essentially every bitrate, which is why it is the better fit for compressing podcast and voice-chat audio to tiny files. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
MMF vs OPUS at a glance
| Aspect | SMAF mobile audio (.mmf) | Opus audio (.opus) |
|---|---|---|
| Format type | Lossy — discards detail it judges invisible to shrink files | Lossy — discards detail it judges invisible to shrink files |
| How it stores data | a chunk-based format conceptually close to MIDI, with score tracks driving FM and wavetable synthesis | the hybrid SILK/CELT design switches coding modes automatically based on content |
| Strongest at | preserving ringtone collections from early-2000s handsets | compressing podcast and voice-chat audio to tiny files |
| Weak spot | no current phone, browser, or OS plays it at all | older car stereos, AV receivers, and MP3 players have never heard of it |
| Metadata | optional contents-info chunks can name the title, artist, and copyright, fields Yamaha included for the commercial ringtone market | vorbis comments in the OpusTags header, including cover art via METADATA_BLOCK_PICTURE, plus an output-gain field used for loudness normalization |
Pick OPUS as the output
Select .opus in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if OPUS is selectable, the route is real and validated.
Convert on your device
Press Convert. The transcode runs on an FFmpeg engine compiled to WebAssembly, so the audio never leaves your device.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid OPUS file. Outputs keep the original filename with the .opus extension.
MMF to OPUS questions, answered
Will converting MMF to OPUS lose quality?
A second lossy step always costs a little, because mmf is lossy-oriented and opus is lossy-oriented and each encoder discards detail differently (generation loss). At the default quality the difference is rarely visible; avoid repeated round-trips between .mmf and .opus.
Is it private to convert MMF files here?
Yes — the .mmf file is processed inside your browser tab and never uploaded. The transcode runs on an FFmpeg engine compiled to WebAssembly, so the audio never leaves your device. Close the tab and the file is gone from memory.
Where will the OPUS file work?
Chrome, Firefox, and Edge have played Opus for a decade and Android supports it natively, while Safari initially accepted the codec only inside CAF or WebM wrappers before extending support to .opus files. Legacy hardware such as older car head units remains the real gap, and conversion to MP3 or AAC bridges it.
Will the OPUS file be bigger or smaller than my MMF?
It depends on the content: the hybrid SILK/CELT design switches coding modes automatically based on content. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my MMF file?
This converter strips container metadata deliberately (the FFmpeg command runs with metadata mapping disabled) so exported files do not leak recording details. In the source, optional contents-info chunks can name the title, artist, and copyright, fields Yamaha included for the commercial ringtone market; none of it is transmitted anywhere because the file never leaves your browser.