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[Bug 19788] What, if any, event should be fired when no key is available to decrypt the block?

From: <bugzilla@jessica.w3.org>
Date: Tue, 30 Oct 2012 22:31:56 +0000
To: public-html-bugzilla@w3.org
Message-ID: <bug-19788-2486-1pD4VRUukd@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=19788

David Dorwin <ddorwin@google.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adrianba@microsoft.com,
                   |                            |strobe@google.com,
                   |                            |watsonm@netflix.com

--- Comment #1 from David Dorwin <ddorwin@google.com> ---
Possible Solution

One option might be to change how we think about the two scenarios. This might
make implementations more difficult but would resolve some of these issues.
* The first algorithm would be “First Time a Key Reference is Encountered.”
Each container would need to specify what this means. For example, ISO
BMFF/CENC might define this as encountering a PSSH even if the PSSH does not
explicitly reference a key. For WebM, this might be when
ContentEncryption/ContentEncKeyID is parsed. For a container without such
headers, it might be the first time each key ID is encountered (i.e. in a
block).
* The second algorithm would continue to be "Encrypted Block Encountered" with
the change that the Key Presence step does not fire an event or an error in the
case where the needed key is not available. Note that this may or may not occur
at the same time as the first reference to a specific key (the first
algorithm).

The first algorithm would be the only one that sends an event, and the second
one would describe the behavior of playback (see bug 18515). Applications would
not be informed that a key is needed for decrypting a current block. They
shouldn’t really need to know for key-related reasons, but are there other
reasons? Would/should existing events (i.e. stalled?) cover any such needs?

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