Convert FLAC to OGG

Ogg is a container and it can hold several codecs; the registry lists Vorbis, Opus and FLAC for it. For twenty-five years `.ogg` has meant Vorbis to most people, because that pairing came first and nothing displaced it in the public imagination. This converter writes Opus, and the difference is worth settling before a batch goes anywhere.

Opus is the stronger codec by any measure — published as RFC 6716 in 2012, it outperforms Vorbis at every bitrate and is mandatory in WebRTC, which is why every browser has one. None of that helps if the receiving side was written to look for Vorbis specifically. Read the project's own wording: a policy that says "Ogg" is satisfied, a policy that says "Ogg Vorbis" is not.

This is the page telling you not to use it, and it applies to more readers than not. Wikimedia Commons accepts FLAC, WAV and Ogg, because the criterion is whether a file can be decoded without a patent licence and FLAC passes it outright. So does every archive that adopted the same reasoning. If you hold a lossless master and the guideline does not name Ogg specifically, the master is the better contribution.

The reason is permanence rather than fidelity today. An archive keeps what it is given and derives everything else from it; a contributed Opus file is a derivative that can never be improved, while a contributed FLAC can be re-encoded into any format anyone needs in twenty years. Convert to Ogg when a rule forces it, when an upload size cap forces it, or when the material is speech where the difference is genuinely inaudible.

Rules naming Ogg were written to keep a project free of formats that need a licensed decoder. Wikimedia's media policy, Debian's packaging rules and the asset guidelines of most open-source games all share that ancestry. Ogg, Vorbis, Opus and FLAC are Xiph formats published as open specifications with royalty-free reference implementations, which is what put them on the acceptable side of the line.

The patent position that produced these rules has softened — MP3's last patents expired in 2017 and much of the MPEG audio estate has followed — but the policies remain, and correctly so from the projects' point of view: a policy written around a specification does not need revisiting every time a patent lapses. If a contribution guideline names Ogg, comply with it rather than arguing the merits in a submission comment.

This is the only lossy encode the recording has taken, which is the best position an encoder can be given: no earlier artefacts to reproduce, no accumulated damage, the full dynamic range of the master to work with. Opus at the Balanced band writes 64 kbps and is genuinely transparent on speech; High quality writes 128 kbps and is generous for music.

It is also irreversible, and an archive is exactly where that matters. Keep the FLAC after converting. The Ogg is a delivery copy for a project with a rule, not a replacement for the thing it was made from, and the whole argument of the previous section collapses if the master gets deleted once the upload succeeds.

Metadata normally loses something at a format boundary. Not here. FLAC stores its tags as Vorbis comments and Ogg carries the same structure in its stream header — an uncomplicated list of uppercase keys with text values — so TITLE, ARTIST, DATE, LICENSE, SOURCE and any custom field you invented arrive on the other side spelled exactly as they were.

That matters more than usual for archive contributions, where the licence statement and the source attribution are not decoration but the reason the file is acceptable. Embedded artwork crosses as a METADATA_BLOCK_PICTURE comment, which is the standard encoding at both ends and what foobar2000, VLC and the media servers read. Nothing has to be re-entered on the upload form that was already correct in the FLAC.

FLAC compresses losslessly to roughly half of raw PCM, which is about 5 to 6 MB a minute at CD quality. Opus at 64 kbps is around 0.5 MB a minute and at 128 kbps around 1 MB. A four-minute recording goes from roughly 22 MB to under 2 MB at Balanced, and a one-hour lecture from about 330 MB to about 29 MB.

For long-form spoken material that difference decides whether an upload is possible at all, and it is the one case where converting away from a lossless master is unarguable. An hour of committee proceedings or a field interview at 64 kbps Opus is indistinguishable from the FLAC to any listener and fits inside limits the FLAC never would.

The three bands resolve inside the encoder and Opus lands far lower than people expect: Small file writes 38 kbps, Balanced 64 and High quality 128. Someone used to judging MP3 sees 64 kbps and assumes the result will be unpleasant. It will not be — Opus at 64 kbps is a comfortable stereo music bitrate and at 38 kbps speech is entirely clear.

For a pronunciation clip, a bird recording, a spoken-word contribution or an oral-history excerpt, Small file is a defensible engineering choice rather than a compromise, and it keeps an archive's storage costs honest. For music, or for anything a project might later want to re-encode, choose High quality and give the encoder the room.

FLAC is specified to a maximum of eight channels, covering mono through 7.1, and the registry records Opus as reaching 255. Nothing in this direction has to be folded down, so a surround or ambisonic FLAC keeps its layout. Mono stays mono, which is the correct outcome for the speech and field recordings that make up most archive contributions.

Sample rate is the one thing that changes. Opus runs on a fixed 48,000 Hz clock and a decoder reports that rate whatever the encoder was handed, so a 44,100 Hz master presents as 48,000 Hz afterwards. No listener will hear it and no archive will object, but a cataloguing pipeline that records the technical rate from the delivered file should be told, because it will not match the master's.

Opus is the one audio target here that needs no encoder download, because every browser had to implement it for calls. The FLAC decoder is likewise on your machine already, so the conversion begins the moment you drop a file and contacts nothing across the network at any point.

Files are capped at 100 MB each — roughly twenty minutes of CD-quality FLAC — and a hundred can be dropped in one go, returned together as a ZIP. For an archive contributor that privacy property is worth stating plainly: the recording becomes public when you choose to upload it to the project, not as a side effect of preparing it.