foo.go

package main

import (
	"crypto/md5"
	"fmt"
	"os"
)

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func main() {
	f, err := os.Open("testorig.mkv")
	check(err)

	_, err = f.Seek(17960960, 0)
	check(err)

	b1 := make([]byte, 3010560)
	n1, err := f.Read(b1)
	check(err)
	m1 := md5.Sum(b1)
	fmt.Printf("offset:17960960 size:%v\t(expected: 3010560)\tmd5:%x (expected: 8abd34cd100b270b824100ebafe6e3fb)\n", n1, m1)

	b2 := make([]byte, 10485760)
	n2, err := f.Read(b2)
	check(err)
	m2 := md5.Sum(b2)
	fmt.Printf("offset:20971520 size:%v\t(expected: 10485760)\tmd5:%x (expected: 762310874c8716000eb81bb1834a8e62)\n", n2, m2)

	b3 := make([]byte, 3280896)
	n3, err := f.Read(b3)
	m3 := md5.Sum(b3)
	check(err)
	fmt.Printf("offset:31457280 size:%v\t(expected: 3280896)\tmd5:%x (ecpected: 1008f316ca473e682ca5f64a648f6e46)\n", n3, m3)

	b := make([]byte, 16777216)
	n := 0
	n += copy(b[0:], b1)
	n += copy(b[3010560:], b2)
	n += copy(b[10485760:], b3)
	m := md5.Sum(b)
	fmt.Printf("offset:17960960 size:%v\t(expected: 16777216)\tmd5:%x (expected: d598e19a67dce51538bd1cafd96ef872)\n", n, m)

}