I solved this by writing reading/writing the MP4 file format directly. Here's the code in VB:
Sub Main()
' Retrieve creation-time and modification-time, embedded inside the metadata of MP4 files
Dim ft = Mp4Times("a.mp4")
Console.WriteLine(ft.CreationTime)
Console.WriteLine(ft.ModificationTime)
' Update those times
Mp4Times("a.mp4", Date.Now, Date.Now)
End Sub
Class FileTimes
Public CreationTime As Date
Public ModificationTime As Date
End Class
Function Mp4Times(fn As String, Optional newCreationTime As Date? = Nothing, Optional newModificationTime As Date? = Nothing) As FileTimes
Dim ft As FileTimes
Using f = If(newCreationTime.HasValue OrElse newModificationTime.HasValue, IO.File.Open(fn, IO.FileMode.Open), IO.File.OpenRead(fn))
f.Seek(0, IO.SeekOrigin.End) : Dim fend = f.Position
' The file is made up of a sequence of boxes, with a standard way to find size and FourCC "kind" of each.
' Some box kinds contain a kind-specific blob of binary data. Other box kinds contain a sequence
' of sub-boxes. You need to look up the specs for each kind to know whether it has a blob or sub-boxes.
' We look for a top-level box of kind "moov", which contains sub-boxes, and then we look for its sub-box
' of kind "mvhd", which contains a binary blob. This is where Creation/ModificationTime are stored.
Dim pos = 0L, payloadStart = 0L, payloadEnd = 0L, boxKind = ""
While ReadNextBoxInfo(f, pos, fend, boxKind, payloadStart, payloadEnd) AndAlso boxKind <> "moov"
pos = payloadEnd
End While
If boxKind <> "moov" Then Return Nothing
pos = payloadStart : fend = payloadEnd
While ReadNextBoxInfo(f, pos, fend, boxKind, payloadStart, payloadEnd) AndAlso boxKind <> "mvhd"
pos = payloadEnd
End While
If boxKind <> "mvhd" Then Return Nothing
' The "mvhd" binary blob consists of 1byte (version, either 0 or 1), 3bytes (flags),
' and then either 4bytes (creation), 4bytes (modification)
' or 8bytes (creation), 8bytes (modification)
' If version=0 then it's the former, otherwise it's the later.
' In both cases "creation" and "modification" are big-endian number of seconds since 1st Jan 1904 UTC
f.Seek(pos + 8, IO.SeekOrigin.Begin) : Dim version = f.ReadByte()
f.Seek(pos + 12, IO.SeekOrigin.Begin)
Dim creationTime As Date, modificationTime As Date
'
If newCreationTime.HasValue Then
creationTime = newCreationTime.Value
If version = 0 Then Write4byteDate(f, creationTime) Else Write8byteDate(f, creationTime)
Else
creationTime = If(version = 0, ReadNext4byteDate(f), ReadNext8byteDate(f))
End If
'
If newModificationTime.HasValue Then
modificationTime = newModificationTime.Value
If version = 0 Then Write4byteDate(f, modificationTime) Else Write8byteDate(f, modificationTime)
Else
modificationTime = If(version = 0, ReadNext4byteDate(f), ReadNext8byteDate(f))
End If
ft = New FileTimes With {.CreationTime = creationTime, .ModificationTime = modificationTime}
End Using
If newCreationTime.HasValue Then IO.File.SetCreationTime(fn, newCreationTime.Value)
If newModificationTime.HasValue Then IO.File.SetLastWriteTime(fn, newModificationTime.Value)
Return ft
End Function
Function ReadNextBoxInfo(f As IO.Stream, pos As Long, fend As Long, ByRef boxKind As String, ByRef payloadStart As Long, ByRef payloadEnd As Long) As Boolean
boxKind = "" : payloadStart = 0 : payloadEnd = 0
If pos + 8 > fend Then Return False
Dim b(3) As Byte
f.Seek(pos, IO.SeekOrigin.Begin)
f.Read(b, 0, 4) : If BitConverter.IsLittleEndian Then Array.Reverse(b)
Dim size = BitConverter.ToUInt32(b, 0)
f.Read(b, 0, 4)
Dim kind = ChrW(b(0)) & ChrW(b(1)) & ChrW(b(2)) & ChrW(b(3))
If size <> 1 Then
If pos + size > fend Then Return False
boxKind = kind : payloadStart = pos + 8 : payloadEnd = payloadStart + size - 8 : Return True
End If
If size = 1 AndAlso pos + 16 <= fend Then
ReDim b(7)
f.Read(b, 0, 8) : If BitConverter.IsLittleEndian Then Array.Reverse(b)
Dim size2 = CLng(BitConverter.ToUInt64(b, 0))
If pos + size2 > fend Then Return False
boxKind = kind : payloadStart = pos + 16 : payloadEnd = payloadStart + size2 - 16 : Return True
End If
Return False
End Function
ReadOnly TZERO As Date = New Date(1904, 1, 1, 0, 0, 0, DateTimeKind.Utc)
Function ReadNext4byteDate(f As IO.Stream) As Date
Dim b(3) As Byte
f.Read(b, 0, 4) : If BitConverter.IsLittleEndian Then Array.Reverse(b)
Dim secs = BitConverter.ToUInt32(b, 0)
Return TZERO.AddSeconds(secs)
End Function
Function ReadNext8byteDate(f As IO.Stream) As Date
Dim b(7) As Byte
f.Read(b, 0, 8) : If BitConverter.IsLittleEndian Then Array.Reverse(b)
Dim secs = BitConverter.ToUInt64(b, 0)
Return TZERO.AddSeconds(secs)
End Function
Sub Write4byteDate(f As IO.Stream, d As Date)
Dim secs = CUInt((d - TZERO).TotalSeconds)
Dim b = BitConverter.GetBytes(secs) : If BitConverter.IsLittleEndian Then Array.Reverse(b)
f.Write(b, 0, 4)
End Sub
Sub Write8byteDate(f As IO.Stream, d As Date)
Dim secs = CULng((d - TZERO).TotalSeconds)
Dim b = BitConverter.GetBytes(secs) : If BitConverter.IsLittleEndian Then Array.Reverse(b)
f.Write(b, 0, 8)
End Sub
-dwith them!) – Dmso