MP4 to FLAC Converter

MP4 to FLAC — What Lossless Actually Buys You

This page extracts the audio track from an MP4 and writes it as FLAC, the Free Lossless Audio Codec. The short answer to the question most people arrive with: an MP4's audio is almost always AAC, which is lossy, so FLAC cannot make it sound better — it can only stop any further loss. Convert to FLAC when the file is going into an archive or an edit that will be re-encoded again later; stay on a lossy format when the file is going into a phone, a car or a message thread.

Side-by-side: What Comes Out of an MP4

Every row below describes the same three minutes of stereo audio at 44.1 kHz, so the sizes are directly comparable. FLAC's figure is a range because lossless compression depends on the material — dense, loud music compresses least, sparse speech compresses most.

The important comparison is the last two rows against FLAC: all three are bit-for-bit reversible, but FLAC typically lands at roughly half the size of raw PCM. If you were reaching for WAV or AIFF purely for losslessness, FLAC gives you the same guarantee for far fewer bytes.

When FLAC Is the Right Target

• You are archiving the audio and expect to re-encode it again later — each lossy generation compounds, and FLAC breaks that chain.
• You are handing audio to an editor, a mastering engineer or a transcription pipeline that wants a lossless input.
• You want an open, patent-unencumbered container: FLAC is standardised as IETF RFC 9639 (December 2024), and its reference implementation is open source.
• You are replacing WAV or AIFF in a library and want the same losslessness at roughly half the storage.

When to Stay Lossy Instead

• The destination is a phone, a car stereo or a chat app — FLAC files are large and support is uneven on older hardware.
• You are publishing a podcast or a lecture recording, where 96-128 kbps AAC is indistinguishable to listeners and a fraction of the size.
• You only need a quick reference copy of the dialogue; MP3 is smaller and plays literally everywhere.
• You expect FLAC to repair a heavily compressed source. It cannot — see the first FAQ below.

How to Convert MP4 to FLAC

1. Upload Your MP4 File: Drag and drop your video, or click "Add Files" to browse. Both .mp4 and .m4v are accepted and several files can be queued with identical settings. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically after a few hours.
2. Set the Compression Level: Open Advanced Options. The Compression level slider runs from 1 to 12 and starts at 12. It controls encoding effort only — the decoded audio is bit-identical at every level, as the on-page note says.
3. Set Audio Channel, Sample Rate and Trim: Leave Audio Channel and Audio Sample Rate on ORIGINAL so the FLAC matches the source exactly; upsampling a lossy track gains nothing. Switch Trim from Unchanged to enter a Start time and Duration if you only want one section.
4. Convert and Download: Click Convert and download the .flac. No sign-up, no watermark.

Choosing a Compression Level

Compression level is the only quality-adjacent control on this page, and it is not a quality control at all — it decides how hard the encoder searches for a smaller representation of audio it must reproduce perfectly either way. There is no bitrate box and no quality preset here, because a lossless codec has no use for one.

The gap between level 1 and level 12 is usually only a few percent of the file, so if a conversion is taking a long time on a long recording, dropping the slider costs you almost nothing.

Frequently Asked Questions

Does converting MP4 to FLAC improve the audio quality?

No. The audio inside an MP4 is nearly always AAC, a lossy codec that permanently discards data during the original encode. FLAC is lossless, but lossless only means it preserves exactly what it is given — it cannot reconstruct detail AAC already threw away. Converting to FLAC prevents further loss on subsequent edits and gives you an open archival container, but the quality ceiling was set by whoever encoded the MP4.

Why is my FLAC file so much larger than the MP4 it came from?

Because the two formats work in opposite directions. The AAC track in your MP4 might have been 128-256 kbps; FLAC stores the full decoded waveform and typically lands around 700-1,000 kbps for 44.1 kHz 16-bit stereo music. That is roughly five times the audio data, even before you account for the fact that FLAC is competing with a format that was designed to be small. The audio is identical; FLAC simply refuses to discard anything.

Does the Compression level change how the FLAC sounds?

No — that is the defining property of a lossless codec. Levels 1 through 12 all decode to bit-identical audio; the slider only changes how much CPU time the encoder spends looking for a more compact representation. Higher levels produce a marginally smaller file and take longer. The on-page note says the same thing: lower is faster and larger, and it does not affect audio quality.

Which compression level should I actually pick?

Leave it at 12 unless you are converting something long and want it finished sooner. The size difference between the fastest and slowest settings is normally only a few percent, so the reasonable strategy is: level 12 for archiving a handful of files, something in the 5-8 range when you are batching a lot of long recordings and encode time starts to matter. There is no setting that trades quality for speed here — only time for a few percent of size.

What sample rate and bit depth does the FLAC output use?

It mirrors the source when Audio Sample Rate and Audio Channel are left on ORIGINAL, which is what you want — video audio is normally 44.1 kHz or 48 kHz, 16-bit, stereo. The format itself is far more permissive than that: RFC 9639 allows 4 to 32 bits per sample, sample rates from 1 Hz to 1,048,575 Hz, and 1 to 8 channels. Resampling a lossy source upward adds bytes without adding information, so changing these values is only worth it when a downstream tool demands a specific rate.

Can I extract just one section of the video's audio?

Yes. Switch Trim from Unchanged and enter a Start time and a Duration, in seconds or as HH:MM:SS.sss. Only that segment is written to the FLAC, which shortens both the conversion and the file. If you would rather cut the video first — useful when you want several separate segments — use the Video Cutter and convert each piece.

Is FLAC actually free to use, or are there patent issues?

FLAC is genuinely free. Its specification is open, its reference implementation is open source, and since December 2024 it has been formally standardised as IETF RFC 9639. That combination is exactly why it is the default choice for long-term audio archiving over lossless formats with murkier licensing histories, and why it turns up in everything from library digitisation projects to hi-res music stores.

What if my MP4 has no audio, or the conversion fails?

Some screen recordings, drone clips and silent exports genuinely contain no audio track — there is nothing to extract, and the conversion will fail rather than hand you a silent file. DRM-protected video (purchased or rented titles) also cannot be decoded. A truncated download can fail for the same reason: the audio index is incomplete. Confirm the source plays sound in a normal player first, then re-upload.

What happens to my video after the conversion?

It is uploaded over an encrypted connection, converted on our servers, and deleted automatically after a few hours. There is no sign-up, no watermark on the output, and your files are never shared or made public. The audio is always decoded and re-encoded into FLAC rather than copied through, which is what makes the output a real lossless file rather than a renamed stream.