init

go.mod

@@ -0,0 +1,3 @@
+module github.com/rixtox/mp4dovi
+
+go 1.17

mp4dovi.go

@@ -0,0 +1,161 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+
+type FourCC [4]byte
+type BoxType FourCC
+
+var (
+	MoovBoxType = BoxType{'m', 'o', 'o', 'v'}
+	TrakBoxType = BoxType{'t', 'r', 'a', 'k'}
+	MdiaBoxType = BoxType{'m', 'd', 'i', 'a'}
+	MinfBoxType = BoxType{'m', 'i', 'n', 'f'}
+	StblBoxType = BoxType{'s', 't', 'b', 'l'}
+	StsdBoxType = BoxType{'s', 't', 's', 'd'}
+	DvheBoxType = BoxType{'d', 'v', 'h', 'e'}
+	Dvh1BoxType = BoxType{'d', 'v', 'h', '1'}
+)
+
+const HeaderSize = 8
+
+type Header struct {
+	Size uint32
+	Type BoxType
+}
+
+func findHeader(r io.ReadSeeker, boxType BoxType, limit int64) (header *Header, err error) {
+	var h Header
+	for offset := int64(0); limit < 0 || offset < limit; offset += int64(h.Size) {
+		if err = binary.Read(r, binary.BigEndian, &h); err != nil {
+			return nil, fmt.Errorf(`failed reading box header: %w`, err)
+		}
+		if h.Type == boxType {
+			return &h, nil
+		}
+		if _, err = r.Seek(int64(h.Size-HeaderSize), io.SeekCurrent); err != nil {
+			return nil, fmt.Errorf(`failed seeking after box "%s": %s`, h.Type, err)
+		}
+	}
+	return nil, fmt.Errorf(`cannot find box "%s"`, boxType)
+}
+
+func forEachBox(r io.ReadSeeker, limit int64, fn func(header Header) error) (err error) {
+	var h Header
+	var start int64
+	if start, err = r.Seek(0, io.SeekCurrent); err != nil {
+		return fmt.Errorf(`failed to get current offset with seek: %w`, err)
+	}
+	for offset := start; limit < 0 || offset < start+limit; offset += int64(h.Size) {
+		if _, err = r.Seek(offset, io.SeekStart); err != nil {
+			return fmt.Errorf(`failed to seek to offset: %w`, err)
+		}
+		if err = binary.Read(r, binary.BigEndian, &h); err != nil {
+			return fmt.Errorf(`failed reading box header: %w`, err)
+		}
+		if err = fn(h); err != nil {
+			return fmt.Errorf(`callback failed: %w`, err)
+		}
+	}
+	return
+}
+
+func sampleEntryHandler(rw *os.File) func(Header) error {
+	return func(h Header) (err error) {
+		if h.Type == DvheBoxType {
+			if _, err = rw.Seek(-4, io.SeekCurrent); err != nil {
+				return fmt.Errorf(`failed to seek back: %w`, err)
+			}
+			if err = binary.Write(rw, binary.BigEndian, Dvh1BoxType); err != nil {
+				return fmt.Errorf(`failed to write box header type "%s": %w`, Dvh1BoxType, err)
+			}
+			fmt.Println(`Changed Dolby Vision codec from dvhe to dvh1`)
+		}
+		return
+	}
+}
+
+func trakHandler(rw *os.File) func(Header) error {
+	return func(trak Header) (err error) {
+		var h *Header
+		var sampleEntryCount uint32
+
+		if trak.Type != TrakBoxType {
+			return
+		}
+
+		if h, err = findHeader(rw, MdiaBoxType, int64(trak.Size-HeaderSize)); err != nil {
+			return fmt.Errorf(`failed finding box "%s": %w`, MdiaBoxType, err)
+		}
+
+		if h, err = findHeader(rw, MinfBoxType, int64(h.Size-HeaderSize)); err != nil {
+			return fmt.Errorf(`failed finding box "%s": %w`, MinfBoxType, err)
+		}
+
+		if h, err = findHeader(rw, StblBoxType, int64(h.Size-HeaderSize)); err != nil {
+			return fmt.Errorf(`failed finding box "%s": %w`, StblBoxType, err)
+		}
+
+		if h, err = findHeader(rw, StsdBoxType, int64(h.Size-HeaderSize)); err != nil {
+			return fmt.Errorf(`failed finding box "%s": %w`, StsdBoxType, err)
+		}
+
+		if _, err = rw.Seek(4, io.SeekCurrent); err != nil {
+			return fmt.Errorf(`failed to seek: %w`, err)
+		}
+
+		if err = binary.Read(rw, binary.BigEndian, &sampleEntryCount); err != nil {
+			return fmt.Errorf(`failed to read sampleEntryCount: %w`, err)
+		}
+
+		if err = forEachBox(rw, int64(h.Size-HeaderSize-8), sampleEntryHandler(rw)); err != nil {
+			return fmt.Errorf(`failed processing sample entry list: %w`, err)
+		}
+
+		return
+	}
+}
+
+func run(mp4file string) (err error) {
+	var (
+		rw *os.File
+		h  *Header
+	)
+	if rw, err = os.OpenFile(mp4file, os.O_RDWR, 0); err != nil {
+		return fmt.Errorf(`cannot open file "%s": %w`, mp4file, err)
+	}
+
+	if _, err = rw.Seek(0, io.SeekStart); err != nil {
+		return fmt.Errorf(`failed to seek: %w`, err)
+	}
+
+	if h, err = findHeader(rw, MoovBoxType, -1); err != nil {
+		return fmt.Errorf(`failed finding box "%s": %w`, MoovBoxType, err)
+	}
+
+	if err = forEachBox(rw, int64(h.Size-HeaderSize), trakHandler(rw)); err != nil {
+		return fmt.Errorf(`failed processing moov children: %w`, err)
+	}
+	return
+}
+
+func help() {
+	fmt.Println(`Usage: mp4dovi <file>`)
+}
+
+func main() {
+
+	if len(os.Args) != 2 {
+		help()
+		os.Exit(1)
+	}
+
+	if err := run(os.Args[1]); err != nil {
+		log.Fatal(err)
+	}
+}