MKV to MP3 converter

Mostly people who record with OBS, which saves MKV unless told otherwise, and want the sound on its own: a stream’s commentary for a podcast, a talk or a lesson to listen back to, a voice-over to transcribe, or a game session’s music. Others have an MKV from a camera, a capture card or a downloaded concert or film and want to listen to it on a phone or in the car. Only convert sound you have the right to use.

An OBS recording can hold up to six audio tracks. A common setup puts everything you hear on track 1, then your microphone alone on track 2 and the game or desktop sound on track 3, so you can balance them later. Players such as VLC or QuickTime play only one, which is why an MKV can seem to have lost your voice when it is simply on another track.

When you drop an MKV here, the converter lists every audio track with the name OBS gave it (“Mic/Aux”, “Desktop Audio”, or Track 1, Track 2 if you never named them), its format and whether it is mono or stereo. Pick one and only that track goes into the MP3. To check you have the right one, convert it and play the MP3; it takes a second or two.

• The whole mix: usually track 1, the one a player picks by default.
• Your voice only, for a podcast, a voice-over or a transcript: the mic track.
• The game or music only, without your commentary: the desktop or game track.

An MKV is a container: a box holding a video track, one or more sound tracks and sometimes subtitles. Most OBS recordings carry AAC sound; films and TV recordings carry Dolby Digital or DTS, and files from free tools often carry Opus or FLAC. The converter decodes the track you picked and encodes it again as MP3. The picture and the subtitles are left behind without being read, which is why a long 1080p recording turns into an MP3 in seconds, and why it works even when the video is HEVC or AV1.

If the sound in the MKV is already MP3, as in some older video files, it is copied across as it is, with no loss and no bitrate to choose. Film sound in 5.1 is mixed down to stereo, because an MP3 holds two channels at most, and the page says so before you convert. Every MP3 is opened again and checked against the length of the original before you can save it.

The bitrate sets the size of the MP3 and how close it comes to the sound in the MKV. It cannot add anything the recording did not have: if OBS recorded the sound at 160 kbps AAC, a 320 kbps MP3 is twice the size of a 160 kbps one and no better.

• 128 kbps: commentary, a talk, a meeting, a lesson. About 1 MB a minute; an hour of stream is 58 MB.
• 192 kbps (the default): game sound, music, or a mix of voice and music. About 1.4 MB a minute.
• 320 kbps: music from lossless OBS sound or a high-quality film track. About 2.4 MB a minute.

If you are going to edit the recording, keep the MKV. It has the picture and every audio track at full quality, and editors that will not open MKV take an MP4, which the MKV to MP4 converter makes in seconds without changing anything. Convert to MP3 last, for listening or sharing.

An MP3 cannot recover a track that was never recorded. If a microphone was not assigned to any track in OBS’s Advanced Audio Properties, its sound is not in the file, and the track list here will show that: no converter can bring it back. Nor will a higher bitrate fix a quiet, clipped or noisy recording; it only makes a larger copy of it.