Audio from video · Windows 10 and 11
Convert MKV to MP3
MKV files often carry surround sound, and sometimes several tracks in different languages. Octoolo turns the sound of an MKV into a stereo MP3 that plays anywhere, never touches the picture, and takes a whole folder of files in one batch.
How to convert MKV to MP3
- 1
Open the tool for sound
Open Converters and click Extract audio. If FFmpeg is not on your PC yet, Octoolo downloads it first: 77 MB, a single time.
- 2
Add the MKVs
Drop the files or their folder. Any MKV with more than one sound track says so on its line, for example “2 sound tracks”.
- 3
Set MP3 and a quality
Choose MP3. For film soundtracks and music, High (320 kbps) is a sensible pick; As it is lands there too for most surround tracks, whose bit rate is far above 320.
- 4
Convert
Start the batch. Each MP3 is written next to its MKV with the same name, and at the end Octoolo tells you how many files were made and how much room they take compared with before.
MKV and MP3 compared
| Detail | MKV | MP3 |
|---|---|---|
| Full name | Matroska Video | MPEG-1 Audio Layer III |
| Holds | Video, several sound and subtitle tracks, chapters | Sound only |
| Plays in | VLC, Windows 10 and 11, Plex, Kodi; iPhones, many TVs, editors and upload forms do not | Every phone, player, car stereo and browser |
| Best for | Films with several languages or subtitles, archiving | Playing and sharing music anywhere |
| Since | 2002, open standard | 1993, Fraunhofer and MPEG |
One MP3, one sound track
An MKV can hold several sound tracks: two languages, a director's commentary, a stereo and a surround mix. An MP3 holds one. Octoolo keeps the first sound track stored in the file and leaves the others out. In most MKVs the first track is the main one, but not in all, and the converter has no way to choose another.
Two ways around that:
- Keep every track. Choose MKA under All 15 sound formats. It is Matroska's sound-only file, and with As it is Octoolo copies every track into it untouched. VLC and most players that read MKV play it.
- Put the track you want first. A tool such as MKVToolNix can rewrite the MKV with its tracks in a new order, without re-encoding anything. Then convert that file to MP3.
Surround sound in a stereo file
Film MKVs often carry 5.1 or 7.1 sound as AC-3, E-AC-3, DTS or TrueHD. MP3 has room for two channels, so Octoolo mixes the surround down to stereo as it converts, folding the center and rear channels into the left and right.
| Sound in the MKV | What Octoolo does |
|---|---|
| MP3, stereo | Copied as it is, with no loss |
| AAC, Opus or Vorbis | Encoded as MP3 |
| AC-3, E-AC-3, DTS or TrueHD surround | Mixed to stereo and encoded as MP3 |
| FLAC or uncompressed | Encoded as MP3, at 320 kbps with As it is |
Want the sound without any loss? Choose FLAC instead. An MKV whose sound is FLAC already is copied untouched, and other sound is stored losslessly from here on, surround channels included.
Where MKV sound is worth keeping
Recording apps such as OBS Studio can save straight to MKV, and many people keep concert films, lectures and long streams in it. Later, the sound alone is often what is wanted:
- A live set or concert film to play as an album, cut into songs with the MP3 cutter.
- A recorded stream or podcast episode, as audio for listeners who will not watch.
- A long lecture, to hear at a quicker pace with audio speed, the pitch kept as it was.
Whatever the reason, the MKV itself is never changed, and the MP3 takes its name, so a folder of episodes or sessions comes out in the same order. If you also want the video in a format phones and editors take, MKV to MP4 keeps the picture and every sound track, usually without re-encoding.
Big files, small results
A two-hour film in MKV can run to many gigabytes, and online converters often cap uploads far below that. Octoolo reads the file where it is, with no size limit, and only the sound is decoded: the picture is passed over, not processed. The MP3 of that two-hour film comes to about 290 MB at High, 170 MB at Balanced and 115 MB at Small.
Some MKVs carry sound at 96 kHz, as TrueHD or FLAC tracks may. An MP3 is made at 48 kHz at most, because lossy formats get nothing out of higher rates, which also keeps the file from growing for no benefit.
A batch of MKVs runs several files side by side, and each line counts its progress and the time left. If an MKV turns out to have no sound at all, it is marked as you add it, so the batch never stops halfway over it.
Octoolo or an online converter?
| Detail | Octoolo | A typical online tool |
|---|---|---|
| Your files | Stay on your computer | Usually uploaded to the site's server |
| Without internet | Works | Does not work |
| File size | No limit | Often capped on free use |
| Many files | Whole folders at once | Often a few at a time |
| Watermarks and ads | None | Common on free plans |
| Cost | $4.99 a month, all 17 apps | Free with limits, or a plan per site |
Questions, answered
Can I pick the language of the MP3?
Not in Octoolo: it takes the first sound track in the file. Reorder the tracks with a tool like MKVToolNix first, or save all of them in an MKA file.
What happens to the subtitles?
They stay in the MKV, which Octoolo never changes. An MP3 is sound only.
Do I need to convert the MKV to MP4 first?
No. Octoolo reads the MKV directly and saves its sound. There is no in-between file.
How long does a film take?
Less than you might expect, because only the sound is decoded and encoded, not the picture. Each file's line shows its speed and the time left while it runs.
Will the stereo mix sound like the film?
Much like a TV playing a surround film on its own two speakers. The center channel, where dialogue usually sits, comes from both sides, and the rear channels fold into the left and right.
Can I set my own bit rate?
Yes. Under More settings, Bit rate goes from 64 to 320 kbps, next to Sample rate and Channels. With Bit rate left on Set by quality, choosing Mono for a talk also halves the rate.
MKV to MP3, and 16 more apps.
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