mvhd.go

package mp4

import (
	"time"
)

type MVHD struct {
	Version      byte
	Flags        [3]byte
	DateCreated  time.Time
	DateModified time.Time

	TimeUnit        uint32 // time unit per second (default = 600)
	DurationInUnits uint64 // time length (in time units)

	Raw []byte // undecoded data after decoded bits above
}

var ErrShortMVHD = formatError("MVHD too short")

func DecodeMVHD(p []byte) (*MVHD, error) {
	m := new(MVHD)

	bp := newBoxParse(p)

	var err error
	m.Version, m.Flags, err = bp.versionFlags()
	if err != nil {
		return nil, err
	}

	m.DateCreated = bp.Date()
	m.DateModified = bp.Date()
	m.TimeUnit = bp.Uint32()
	m.DurationInUnits = bp.UintVar()

	if bp.Short() {
		return nil, ErrShortMVHD
	}

	r := bp.Rest()
	if len(r) != 0 {
		m.Raw = make([]byte, len(r))
		copy(m.Raw, r)
	}
	return m, nil
}

// encoded length in bytes
func (m *MVHD) Len() int {
	l := 20 + len(m.Raw)
	if m.Version == 1 {
		l += 12
	}
	return l
}

func (m *MVHD) Duration() time.Duration {
	return time.Duration(m.DurationInUnits) * time.Second / time.Duration(m.TimeUnit)
}

/* MVHD http://xhelmboyx.tripod.com/formats/mp4-layout.txt

   * 8+ bytes movie (presentation) header box
       = long unsigned offset + long ASCII text string 'mvhd'
     -> 1 byte version = 8-bit unsigned value
       - if version is 1 then date and duration values are 8 bytes in length
     -> 3 bytes flags =  24-bit hex flags (current = 0)

     -> 4 bytes created mac UTC date
         = long unsigned value in seconds since beginning 1904 to 2040
     -> 4 bytes modified mac UTC date
         = long unsigned value in seconds since beginning 1904 to 2040
     OR
     -> 8 bytes created mac UTC date
         = 64-bit unsigned value in seconds since beginning 1904
     -> 8 bytes modified mac UTC date
         = 64-bit unsigned value in seconds since beginning 1904

     -> 4 bytes time scale = long unsigned time unit per second (default = 600)

     -> 4 bytes duration = long unsigned time length (in time units)
     OR
     -> 8 bytes duration = 64-bit unsigned time length (in time units)

     -> 4 bytes decimal user playback speed = long fixed point rate (normal = 1.0)
     -> 2 bytes decimal user volume = short fixed point level
         (mute = 0.0 ; normal = 1.0 ; QUICKTIME MAX = 3.0)
     -> 10 bytes reserved = 5 * short values set to zero
     -> 4 bytes decimal window geometry matrix value A
         = long fixed point width scale (normal = 1.0)
     -> 4 bytes decimal window geometry matrix value B
         = long fixed point width rotate (normal = 0.0)
     -> 4 bytes decimal window geometry matrix value U
         = long fixed point width angle (restricted to 0.0)
     -> 4 bytes decimal window geometry matrix value C
         = long fixed point height rotate (normal = 0.0)
     -> 4 bytes decimal window geometry matrix value D
         = long fixed point height scale (normal = 1.0)
     -> 4 bytes decimal window geometry matrix value V
         = long fixed point height angle (restricted to 0.0)
     -> 4 bytes decimal window geometry matrix value X
         = long fixed point positon (left = 0.0)
     -> 4 bytes decimal window geometry matrix value Y
         = long fixed point positon (top = 0.0)
     -> 4 bytes decimal window geometry matrix value W
         = long fixed point divider scale (restricted to 1.0)
     -> 8 bytes QUICKTIME preview
         = long unsigned start time + long unsigned time length (in time units)
     -> 4 bytes QUICKTIME still poster
         = long unsigned frame time (in time units)
     -> 8 bytes QUICKTIME selection time
         = long unsigned start time + long unsigned time length (in time units)
     -> 4 bytes QUICKTIME current time = long unsigned frame time (in time units)
     -> 4 bytes next/new track id = long integer value (single track = 2)
*/