You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: chunk.go
    path of file: ./repos/photoprism/pkg/video
    
    the code of the file until where you have to start completion: package video

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"os"

	"github.com/photoprism/photoprism/pkg/fs"
	"github.com/sunfish-shogi/bufseekio"
)

// Chunk represents a fixed length file chunk.
type Chunk [4]byte

// Get returns the chunk as byte array.
func (c Chunk) Get() [4]byte {
	return c
}

// Hex returns the chunk as hex formatted string.
func (c Chunk) Hex() string {
	return fmt.Sprintf("0x%x", c[:])
}

// String returns the chunk as string.
func (c Chunk) String() string {
	return string(c[:])
}

// Bytes returns the chunk as byte slice.
fu
    
func (c Chunk) DataOffset(file io.ReadSeeker) (int, error) {
	if file == nil {
		return -1, errors.New("file is nil")
	}

	data := c.Bytes()
	dataSize := len(data)
	blockSize := 128 * 1024
	buffer := make([]byte, blockSize)

	// Create buffered read seeker.
	r := bufseekio.NewReadSeeker(file, blockSize, dataSize)

	// Index offset.
	var offset int

	// Search in batches.
	for {
		n, err := r.Read(buffer)
		buffer = buffer[:n]

		if err != nil {
			if err != io.EOF {
				return -1, err
			}

			break
		} else if n == 0 {
			break
		}

		// Return data index, if found.
		if i := bytes.Index(buffer, data); i >= 0 {
			return offset + i, nil
		}

		offset += n
	}

	return -1, nil
}