A converter that tells you when not to.

AIFF for anything going into Rekordbox or onto a stick — it is lossless, every CDJ in service reads it, and unlike WAV it holds artist and title tags reliably. FLAC for the archive at home, because it stores identical audio in about a third less space. MP3 at 320 when the stick is full or the track is being sent to somebody. The only format on that list you should never convert *into* from a lossy source is MP3.

It depends entirely on which way you cross the lossless line, and there are only three cases. Lossless to lossless — WAV, AIFF and FLAC between each other — is exact and reversible, so nothing is lost. Lossless to MP3 throws audio away permanently, which is fine as the last step in a chain and bad as a middle one. Lossy to lossless makes a file ten times bigger and recovers precisely nothing, which is the most common misunderstanding in this whole area.

No. Everything happens inside this browser tab — the file is decoded, re-encoded and handed back without a single network request, which you can confirm by opening the network panel and watching it stay empty. There is no server behind this page, so an unreleased promo is safe to drop on it and nothing is left in anybody's storage afterwards.

Yes, and that is the reason to use it rather than a site that does one file at a time behind an upload. Drop as many files as you like, choose the target once, and the queue runs through them with a report for each — what it came from, what it became, and how the sizes compare. The set comes back as a single archive rather than as thirty separate downloads.

Yes, and it was checked rather than assumed. Every test file was encoded, decoded again by an independent decoder, and compared byte for byte against the original samples — zero differences on all of them, including 24-bit, mono, digital silence and hard-clipped material. Each file also carries a checksum of its own audio, so it can prove years later that it is still the recording it started as. On real records the output lands near 67% of the uncompressed size, between the standard encoder's default setting and its slowest.

Because nothing in a DJ chain wants AAC as an output — you convert *from* an M4A because that is what an Apple purchase arrives as, not to one. There is also a practical reason: encoding AAC in a browser only works in Chrome and Edge, so the feature list would be different depending on what you opened the page in, which is worse than not offering it.

They are streaming and voice codecs and no CDJ reads either of them. A DJ converting *to* one has almost certainly misunderstood something, and a DJ converting *from* one is working from a stream rip that has bigger problems than its container. Leaving them out is a decision rather than a gap.

320, for anything you will play out. The difference between 320 and 256 is genuinely small; the difference between 320 and 192 shows up on a big system as a dull top end exactly where hi-hats and air live. A four-minute track at 320 is about 9 MB, so a 64 GB stick still holds thousands — the space a lower bitrate saves buys you nothing you actually need.

Tags do. Artist, title, album, genre, year, label, BPM, key, comment and the cover art are read off the source and written into the output, whichever pair of formats you picked — so a converted folder arrives in Rekordbox named rather than as a wall of filenames. Cue points do not, and cannot: they live in Rekordbox's own database against the original file rather than inside it, so converting does not delete them but Rekordbox will treat the output as a new file and not connect the two. Convert first, then analyse and grid.

By where the audio stops. A lossy encoder discards everything above a ceiling that depends on its bitrate, and that ceiling survives every later conversion — so a "lossless" file whose content stops dead at 16 kHz was an MP3 at some point and somebody re-wrapped it. The converter measures that ceiling on lossless sources and says so in the report, which is a thing no other converter will tell you.