[Mp4-tech] MPEG format test

[Dave Singer]

At 12:57 PM -0500 8/12/04, Anil Gupte wrote:
>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

the mpeg-4 file format does not encrypt the structure of the file, 
only the media data.  we were under the impression you were the 
author of the encryption/decryption system and wanted to validate, 
and that you were using, and knew, the mpeg-4 file format (this being 
an mpeg-4 list).  we might have been wrong on both counts;  can you 
say more?
>
>
>----- Original Message -----
>From: <mailto:ssingh neomagic.com>Shailendra Singh
>To: <mailto:singer apple.com>Dave Singer
>Cc: <mailto:anil-list maxnetwork.com>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:
>
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>>	PADDING-BOTTOM: 0px; PADDING-TOP: 0px } UL { 
>>	PADDING-BOTTOM: 0px; PADDING-TOP: 0px } OL { 
>>	PADDING-BOTTOM: 0px; PADDING-TOP: 0px } LI { 
>>	PADDING-BOTTOM: 0px; PADDING-TOP: 0px }
>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: <mailto:singer apple.com>Dave Singer
>>
>>To: <mailto:anil-list maxnetwork.com>Anil Gupte ; 
>><mailto:mp4-tech lists.mpegif.org>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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>
>_______________________________________________
>NOTE: Please use clear subject lines for your posts. Include [audio, 
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>
>
>
>--
>
>David Singer
>Apple Computer/QuickTime
>
>
>_______________________________________________
>NOTE: Please use clear subject lines for your posts. Include [audio, 
>[video], [systems], [general] or another apppropriate identifier to 
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>
>Note: Conduct on the mailing list is subject to the Antitrust 
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><http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php>http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php

-- 
David Singer
Apple Computer/QuickTime
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