# MKV merge audio

## Extract audio from MP4 movie file
```
ffmpeg -i input_dubbing_PL.mp4 -vn --codec copy pl_audio.aac
```

Note: `-vn` option means _no video_. Only audio is being extracted.


## Add second audio track to existing MKV file
The following command will create the file `output.mkv` with two audio tracks:
* `pl` - the track to be added
* `en` - original audio track existing in `input.mkv` movie file.

```bash
mkvmerge -o output.mkv --language 0:pl pl_audio.aac --language 1:en input.mkv
```