Read magic number

Question

Read magic number

Peter Volz 1,295

Hello,

I have problem understanding one particular file type here:

https://en.wikipedia.org/wiki/List_of_file_signatures

ts MPEG Transport Stream (MPEG-2 Part 1)

Magic number hex signature is only 1 byte: &H47 / G

But there are notes I cannot figure out:

0

0xBC

0x178

...

(every 188th byte)

I use:

ReadByte.Take(1).SequenceEqual({&H47})

Anyone knows how to cover this type?

Thanks in advance :)

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Answer 1

Jiachen Li-MSFT 34,221 Microsoft External Staff

Hi @Peter Volz ,

In the context of MPEG Transport Stream (MPEG-TS) files, where the packet size is typically 188 bytes, the offset refers to the starting positions of individual MPEG-TS packets within the file.

So 47 appears at every 188th byte, judging only the 47 at the beginning of a file can lead to confusion with other file types.

Best Regards.

Jiachen Li

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Peter Volz 1,295 Reputation points

2024-03-11T08:07:22.7333333+00:00

Thanks, so will need to read the whole file? btw, how to get each 188th byte? :(

Jiachen Li-MSFT 34,221 Microsoft External Staff

Hi @Peter Volz ,

You can choose to determine whether it is another file format starting with 47 and exclude other possibilities.

And here is the code for getting each 188th byte.

        Dim filePath As String = "pmpeg_ts_file.ts"

        Using fs As New FileStream(filePath, FileMode.Open, FileAccess.Read)
            Dim buffer(187) As Byte ' MPEG-TS packets are typically 188 bytes long

            ' Read the file in chunks of 188 bytes
            While fs.Read(buffer, 0, buffer.Length) > 0
                If buffer(0) = &H47 Then
                    Console.WriteLine("Found MPEG-TS packet at position: " & fs.Position)
                End If

            End While
        End Using

Peter Volz 1,295 Reputation points

2024-03-11T09:05:17.77+00:00

Thanks, just one thing, I already have the file as Stream so omitted the Using fs As New FileStream...

While (bytesRead = InputStream.Read(buffer, 0, buffer.Length)) > 0

Option Strict On disallows implicit conversions from 'Boolean' to 'Integer'

Why the code had no error with FileStream and returns this error with Stream? :(
Peter Volz 1,295 Reputation points

2024-03-11T09:52:07.5866667+00:00

Beside that, debugging the code will never enter inside the While loop.

Means that:

(bytesRead = fs.Read(buffer, 0, buffer.Length)) > 0

is never met :(

Please help :(
Jiachen Li-MSFT 34,221 Reputation points Microsoft External Staff

2024-03-12T02:39:18.6033333+00:00

Hi @Peter Volz ,

I've modified and simplified the code, and you can check out the new code.

In this code, Stream should work the same as FileStream.
Peter Volz 1,295 Reputation points

2024-03-12T11:59:56.6533333+00:00

Thanks man, it works :)

But I'm going to use it to detect if a file is TS format.

So how to make sure if the file is ts? this will show some TS packet positions.
Jiachen Li-MSFT 34,221 Reputation points Microsoft External Staff

2024-03-13T01:12:10.4766667+00:00

Hi @Peter Volz ,

Like I mentioned above, you can use the elimination method to determine if this file matches the magic number of other file types that start with &h47.

Or iterate through the entire file to see if &H47 is true at every 188th byte.

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