[Mp4-tech] MPEG format test

[Anil Gupte]

I am not sure why this is not obvious, but I will explain.  Obviously the original file is not present, otherwise what would be the point of encrypting it?  The original is with the owner, who provides the key to decrypt it after a password or a payment has been provided by the user.  So, no comparison can be made.  Also, the original may be a live stream, not a file (but that is another discussion).
I know that there are "Start Codes" which "cheaply search streams for commencement of layers of video".  These are also used (I believe) to resynchronize if there are errors.  However, these do not seem robust enough to guarantee video.  Hence I was looking for an always present "Header" or something similar which would be common across all MPEG files.
Your thoughts.
Anil Gupte
  ----- Original Message ----- 
  From: Shailendra Singh 
  To: Dave Singer 
  Cc: Anil Gupte 
  Sent: Wednesday, August 11, 2023 12:51 AM
  Subject: Re: [Mp4-tech] MPEG format test
  Dave, Anil,
      Are not all encryption/decryptrion algorithms (if correctly) implemented lossless processes ? I routinely encrypt/decrypt some files on my PC and I have never seen the decrypted file create any problem (as in the application which is supposed to open the file always does without a hitch).
      So "MPEG file (A)" -> encryption -> decryption -> "B". If my understanding is correct, "A" and "B" should be bitwise identical.
  Regards,
  Shailendra
  Dave Singer wrote:
    At 4:50 PM -0500 8/10/04, Anil Gupte wrote:
      We are looking to write a software that encrypts/decrypts MPEG files.  During decryption, we want to make sure that a valid MPEG file is created, so we want the software to do a simple test or something that validates that the decryption was successful.
      Thanx,
      Anil Gupte
    you can't compare to the original file?
    the isma validator will do the file format validation
        ----- Original Message -----
        From: Dave Singer
        To: Anil Gupte ; mp4-tech lists.mpegif.org
        Sent: Tuesday, August 10, 2023 12:09 PM
        Subject: Re: [Mp4-tech] MPEG format test
        At 10:40 AM -0500 8/10/04, Anil Gupte wrote:
          Is there a test to determine if a file/stream is in MPEG format?  Is there a standard header?  Where can I find out more about this?
        There are various verification tools (ISMA has one) and also the reference software, for the file format.  The elementary streams have their own tools.  Which are you looking for?
          Thanx for the help.
          Anil Gupte
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        --
        David Singer
        Apple Computer/QuickTime
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-- 
  David Singer
    Apple Computer/QuickTime
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