MKV to FLAC Converter

MKV to FLAC: Will the Result Actually Be Lossless?

This tool takes the audio out of a Matroska (.mkv) video and writes it as FLAC, discarding the picture. The question almost everyone is really asking is whether the result is "lossless", and the honest answer depends entirely on what is inside your MKV. FLAC never adds loss — but it also cannot undo loss that already happened. If the MKV carries a lossless track, you get a bit-perfect copy. If it carries AC-3, DTS or AAC, you get a lossless container wrapped around audio that was already lossy, at a much larger size. Both are legitimate; knowing which one you are doing is the point of this page.

What Your MKV's Audio Codec Means for the Result

Matroska can carry almost any audio codec, so check the source before assuming bit-perfect output. Media players and tools like MediaInfo will tell you which codec a track uses:

Choose FLAC When

• The MKV's audio is genuinely lossless — a concert capture, a Blu-ray rip with TrueHD or DTS-HD MA, or a PCM master. This is the case FLAC exists for.
• You are archiving. FLAC is open, royalty-free and formally specified, so a file you make today stays readable. It is standardised as RFC 9639, published in December 2024.
• You will edit or re-encode later. Every subsequent encode starts from an intact waveform instead of compounding lossy generations.
• You want tags and clean metadata. FLAC's tagging is well supported across audio software in a way that a raw stream pulled out of a container is not.

Choose Something Else When

• The source is lossy and you just want a portable file. Wrapping a 192 kbps AC-3 stream in FLAC can produce a file several times larger with no audible gain — MKV to MP3 is the sane choice for listening.
• You need maximum device compatibility. Car heads-units, older phones and some smart speakers still refuse FLAC.
• You are feeding an editor that wants uncompressed audio. MKV to WAV hands most DAWs and video editors exactly what they expect with no decode step.
• You only need a short excerpt for a clip or a ringtone. Encode it small; lossless is wasted on a fifteen-second cut.

How to Convert MKV to FLAC

1. Upload Your MKV File: Drag the .mkv onto the page or click "+ Add Files". Batch uploads are supported and each file is converted with the same settings.
2. Set the Compression Level: The Compression level slider runs from 1 to 12 and starts at 12. As the page's own note says, a lower number is faster but produces a larger file — and it does not affect the audio either way.
3. Leave Sample Rate and Channels Alone Unless You Need To: Audio Sample Rate and Audio Channel both start on ORIGINAL, which copies the source faithfully. Change them only deliberately — resampling or folding to mono breaks the bit-perfect chain. Trim starts on Unchanged if you only want a section.
4. Convert and Download: Click Convert and download the .flac. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically a few hours later — no sign-up, no watermark.

FLAC vs WAV vs MP3 as an Extraction Target

Frequently Asked Questions

Is converting MKV to FLAC actually lossless?

The FLAC step always is; the overall chain depends on the source. FLAC is a lossless codec — RFC 9639 defines it around the property that "decompressing losslessly compressed information returns exactly the original data" — so encoding decoded audio to FLAC never discards a sample. If the MKV holds FLAC, PCM, Dolby TrueHD or DTS-HD Master Audio, the output is bit-perfect. If it holds AC-3, DTS core, AAC or MP3, those bits were thrown away by the original encoder years ago and nothing can bring them back. Wrapping lossy audio losslessly is still lossy audio — just bigger.

Why is my FLAC larger than the audio track it came from?

Because FLAC stores the full decoded waveform, not the compact lossy representation. A 192 kbps AC-3 track decodes to a 48 kHz multi-channel PCM stream; FLAC then compresses that stream by roughly 30–50%, but it is compressing something far larger than the AC-3 was. The result can easily be several times the size of the original track while sounding identical to it. That is expected behaviour, not a bug — and it is the strongest argument for using MKV to MP3 when the source was lossy to begin with.

Does the Compression level slider change how it sounds?

No. It only changes how hard the encoder works and how long it takes. The page states this directly in its own help note: a lower number is faster but leaves a larger file, and it "doesn't effect the audio quality". Level 1 and level 12 decode to exactly the same waveform — every level is lossless, so the only trade is encode time against a few percent of file size. Level 12 (the starting value) is the right choice for archiving; drop it if you are converting a long file and want it finished sooner.

My MKV has 5.1 surround — does that survive?

It can. FLAC supports 1 to 8 channels per RFC 9639, so a 5.1 track can be carried through as 5.1 when Audio Channel is left on ORIGINAL. Deliberately choosing MONO or STEREO downmixes instead, which is a one-way change you cannot undo later. If you are archiving a surround soundtrack, leave both Audio Channel and Audio Sample Rate on ORIGINAL — any resampling or downmix converts a bit-perfect job into an approximation.

Which audio track gets converted if my MKV has several?

The one the container marks as its default audio track. There is no track picker on this page, so a film with an original-language track plus dubs and a commentary produces a single FLAC from whichever stream is flagged default. Subtitles, chapters and the video itself are all discarded — FLAC is an audio-only format. If you need a specific alternate track, remux the MKV first with that stream set as default and then convert.

What actually happens to the audio during conversion?

In our pipeline the audio stream is decoded to PCM and then re-encoded with the FLAC encoder at your chosen compression level — it is a genuine encode, not a stream copy, so the output is a real FLAC file rather than the original codec under a new extension. The FLAC encode itself is mathematically lossless: what goes in as decoded samples comes back out identically when the file is played. That is exactly why a lossless source survives untouched while a lossy source is preserved rather than repaired.

What plays FLAC files?

Very broad support, with a few gaps worth knowing. VLC, foobar2000, mpv, Kodi and essentially every desktop media player handle FLAC natively, as do Android and modern hi-res audio players. Apple's ecosystem reads FLAC through the Files app and supports it in recent releases, though ALAC has historically been the preferred lossless format there. The remaining holdouts tend to be car stereos, older Bluetooth speakers and budget devices. If something refuses your file, FLAC to MP3 makes a universally playable copy.

Can I extract just part of a long recording?

Yes, in two ways. Open Trim on this page — it starts on Unchanged — and enter a start time and duration to encode only that span, which is faster than converting a two-hour concert and cutting afterwards. Alternatively, cut the finished audio with the Audio Cutter, or trim the source video first with the Video Cutter if you want to keep a video copy of the excerpt as well.

What happens to my file after conversion?

Your MKV is uploaded over an encrypted connection, converted on our servers, and both the upload and the resulting .flac are deleted automatically a few hours later. Files are never shared or made public, there is no sign-up, and nothing is added to the audio. The original file on your device is untouched — the FLAC is written as a new file for you to download.