import (
    "os"
    "fmt"
    "github.com/pixelbender/go-matroska/matroska"
)

func main() {
    doc, err := matroska.Decode("example.mkv")
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(doc.Segment.Info[0].Duration)
}