[Mp4-tech] MPEG format test
Anil Gupte
anil-list maxnetwork.com
Fri Aug 13 03:03:58 EDT 2004
Re: [Mp4-tech] MPEG format testYes, we are the author of the encryption decryption system, but the decrypting process is separate and done by a user different from the encryptor. The point is, we are encrypting to prevent access to the file unless authorized. If we keep the original next to it so it can compared, then the encryption serves no purpose.
And, yes, we know a little bit about the MPEG format, but we are just starting to work with it, so we are not familiar with it. We have not written any code to read/write MPEG, we are simply planning it right now. That is why I had to ask of the MPEG format has a header that is common to all MPEG files.
I think Rob Koenen has mostly answered what we needed to know, although I did not understand his answer completely.
Thanx,
Anil Gupte
----- Original Message -----
From: Dave Singer
To: Anil Gupte ; mp4-tech lists.mpegif.org ; Shailendra Singh
Sent: Thursday, August 12, 2023 12:59 PM
Subject: Re: [Mp4-tech] MPEG format test
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: 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:
BLOCKQUOTE { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } DL { 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: 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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NOTE: Please use clear subject lines for your posts. Include [audio, [video], [systems], [general] or another apppropriate identifier to indicate the type of question you have.
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NOTE: Please use clear subject lines for your posts. Include [audio, [video], [systems], [general] or another apppropriate identifier to indicate the type of question you have.
Note: Conduct on the mailing list is subject to the Antitrust guidelines found at http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php
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David Singer
Apple Computer/QuickTime
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_______________________________________________
NOTE: Please use clear subject lines for your posts. Include [audio, [video], [systems], [general] or another apppropriate identifier to indicate the type of question you have.
Note: Conduct on the mailing list is subject to the Antitrust guidelines found at http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php
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David Singer
Apple Computer/QuickTime
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