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Re: CfC: to publish Encrypted Media Extensions specification as a First Public Working Draft (FPWD)

From: Glenn Adams <glenn@skynav.com>
Date: Fri, 1 Feb 2013 08:56:23 -0700
Message-ID: <CACQ=j+eCb2c1qr8UuK_Gpf0qG1dOHkeeAeu2teLkJqhic+SgHw@mail.gmail.com>
To: "L. David Baron" <dbaron@dbaron.org>
Cc: robert@ocallahan.org, Sam Ruby <rubys@intertwingly.net>, public-html-admin@w3.org
On Thu, Jan 31, 2013 at 8:48 PM, L. David Baron <dbaron@dbaron.org> wrote:

> On Thursday 2013-01-31 16:39 -0700, Glenn Adams wrote:With CDMs, on the
> other hand, the data communicated between parties
> is the tuple (encrypted data, key system).  This means the
> underlying data are meaningless unless both parties know what the
> key system is.  This, in turn, is why it's important that the key
> systems or the content decryption modules implementing them be
> registered.
>

>From the content authoring perspective as well as actual function of EME,
the only reason to employ a registry is to prevent name collisions for key
string identifiers. Since EME defines use of reversed DNS identifiers, then
this implicitly satisfies that requirement.

>From the perspective of UA implementers, a registry containing additional
information -- e.g., a full or partial specification of the key system, a
contact point for obtaining additional information or licensing, etc. --
would only be needed if a UA wished to directly implement a CDM that
supported some key system. Alternatively, a UA implementer could provide an
Add-On/Extension mechanism to permit system administrator or end user
installation of a CDM implementation supplied by a third party.

For example, let's say I sign up for a first release HD video service that
encrypts its media streams. That sign-up service may entail determining if
my UA supports certain media types and certain key systems. If it does not
support the required key system, then it may ask me to authorize
downloading an Add-On/Extension that does support it. If I don't authorize
it, or if the UA does not support downloading a CDM, then the service
provider may choose instead to use one of the built-in CDMs supported by
the UA as determined when querying support for media types and key systems.
If the service provider doesn't find an acceptable supported CDM, then it
may offer a lower level service, such as non-HD or non-first release, etc.

Do you believe this scenario is infeasible given the current design of EME?
Received on Friday, 1 February 2013 15:57:11 GMT

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