5 min read
Extract audio from MKV: picking the right stream every time
An MKV can hold a dozen audio streams. Extraction is easy; picking the correct one is where projects go wrong.
Matroska was designed to carry everything at once, which makes it excellent for archive delivery and treacherous for anyone extracting audio in a hurry. The first stream is not necessarily the original language, and the highest channel count is not necessarily the one you should conform to.
Read the stream table first
- Language tag: eng, fra, und. An untagged stream is a warning, not a default.
- Channel count: 2 for stereo, 6 for 5.1, 8 for 7.1.
- Codec: FLAC and PCM extract losslessly, AC3 and AAC need a decode.
- Track name: archives often label commentary, described audio and clean effects here.
Extracting more than one
For a restoration or a re-version, you usually need several streams. Extract them one at a time and put the language and channel count in every filename, otherwise the session becomes an identification exercise.
Surround streams in an editorial timeline
A 5.1 stream imported into a stereo timeline will be folded by whatever rule the software applies. Decide the downmix yourself, with known gains, so dialogue level survives the fold.
Keeping it local
Archive material is often under licence restrictions that forbid third party hosting. Browser based extraction keeps the file on your machine, which keeps the paperwork simple.