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Re: [rtcweb] On video codec for rtcweb

Martin Thomson <martin.thomson@gmail.com> Fri, 23 March 2012 15:22 UTC

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Date: Fri, 23 Mar 2012 08:21:58 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: "Timothy B. Terriberry" <tterriberry@mozilla.com>
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Cc: rtcweb@ietf.org
Subject: Re: [rtcweb] On video codec for rtcweb
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On 23 March 2012 05:34, Timothy B. Terriberry <tterriberry@mozilla.com> wrote:
> With a direct browser-to-browser connection, there is nothing sitting
> between them to do the transcoding. In the DTLS-SRTP case with identity
> verification, which I think a number of people here view as highly
> important, you are in fact _guaranteeing_ that nothing but the browser can
> encode or decode the video.

This is incorrect.  The browser can implement the DTLS handshake and
crypto renegotiation, plus the SRTP shim.  It is possible for the
browser to perform the crypto without performing encode or decode if
the source is capable of providing RTP.  From RFC 3711:

   [...]  Conceptually, we consider SRTP to be a "bump in the stack"
   implementation which resides between the RTP application and the
   transport layer.  SRTP intercepts RTP packets and then forwards an
   equivalent SRTP packet on the sending side, and intercepts SRTP
   packets and passes an equivalent RTP packet up the stack on the
   receiving side.

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