Re: [rtcweb] Followup to discussion of O/A and codecs from Friday session

Roman Shpount <> Fri, 08 April 2016 22:21 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id D568D12D51C for <>; Fri, 8 Apr 2016 15:21:26 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.6
X-Spam-Status: No, score=-2.6 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id 8-Ix9nV5neuw for <>; Fri, 8 Apr 2016 15:21:25 -0700 (PDT)
Received: from ( [IPv6:2607:f8b0:4001:c06::234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 2756712D11F for <>; Fri, 8 Apr 2016 15:21:25 -0700 (PDT)
Received: by with SMTP id g185so148007060ioa.2 for <>; Fri, 08 Apr 2016 15:21:25 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20150623; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc; bh=S7yMFO9uhrhiV+bzQzgb1egAfWEpzYXPNa4IoopeNb4=; b=O2P0mnSWSW5vxYTYWKPgKiJyyus0SWbimm6TWy9SxPVcWahcCzm/PsH2aLjuiGo5GX bocBFhhSchBTNS7i/KvPONAHxxckyXukw4id06HjmUgdKEij3eXmzXeTZOnx2gnOMD7Q mbY081+F6mEV2P3D04dwtbdEeNU/FPBE2lPrQ89fUnMJZCny1wgNi6MluZJRBdoqCVvk dxjsHhNdlocLZIq9ASyPflBRKAS+EaKKOVJKfdWQPsdD6+QXxSK9Ik+tu7G8EHlseSyE X0aFc09CVO30DSk/ulD+Z8dwQkkDF59BijtteCpv2WtAmGBLmgGNOrgHOhe2KIzZYAaD 8X1w==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc; bh=S7yMFO9uhrhiV+bzQzgb1egAfWEpzYXPNa4IoopeNb4=; b=VE9NZDKkfGsiwdCgQumlCV0R3oTUBra7uka6TMA/tdjGhrAKj2fhaQJ/1hUmUHLORO CF+2Wh09OfoXkRMIZ2C0Hod+8K8FOIHU+1l7r3HbhqHC32iFAsagSzj39J7CWcsj9UNs f8HW1LARXVUbtpBjBJX2O5MluQFXNdtnQmchVJFGSGKY0bwhJRTP7/xI5x5X3UroF887 Vr6fADEb2fkyuQbfp07o+dXCWTVgoDEE0waYIlu4fpwLIwjgJgzpEIntoZiqEZLQGIVc uPudsFj9JQfZA3VRGxE/UOv1w++67TU9lyvX8vjMQ3QpaZzlyND2FEo+yCfMCwKWGf4u jHew==
X-Gm-Message-State: AD7BkJIO95fKpssrhbQzmH0aGf8Pxg6hU5WHm8Z6Bh/smpJe+XkjW/rYD37qHRLoj0SCxQ==
X-Received: by with SMTP id o75mr13521731ioe.56.1460154084576; Fri, 08 Apr 2016 15:21:24 -0700 (PDT)
Received: from ( []) by with ESMTPSA id au6sm3837290igc.0.2016. for <> (version=TLSv1/SSLv3 cipher=OTHER); Fri, 08 Apr 2016 15:21:24 -0700 (PDT)
Received: by with SMTP id o126so125675261iod.0 for <>; Fri, 08 Apr 2016 15:21:23 -0700 (PDT)
MIME-Version: 1.0
X-Received: by with SMTP id g67mr11043965ioe.38.1460154083724; Fri, 08 Apr 2016 15:21:23 -0700 (PDT)
Received: by with HTTP; Fri, 8 Apr 2016 15:21:23 -0700 (PDT)
In-Reply-To: <>
References: <> <>
Date: Fri, 08 Apr 2016 18:21:23 -0400
X-Gmail-Original-Message-ID: <>
Message-ID: <>
From: Roman Shpount <>
To: Harald Alvestrand <>
Content-Type: multipart/alternative; boundary="001a1140b4727a580c0530009d58"
Archived-At: <>
Cc: "" <>
Subject: Re: [rtcweb] Followup to discussion of O/A and codecs from Friday session
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Real-Time Communication in WEB-browsers working group list <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Fri, 08 Apr 2016 22:21:27 -0000

On Fri, Apr 8, 2016 at 6:01 PM, Harald Alvestrand <>

> This indicates that the answer's omission of a codec does not allow the
> offerer to deallocate resources that it has reserved for decoding that
> type of stream (such as hardware).
> Under this interpretation, if I reserve hardware for decoding VP8 and
> H.264, and I get back an answer that indicates VP8 only, I cannot
> deallocate my H.264 resources, since the answerer may choose to send me
> H.264 anyway.
Based on what I heard from multiple people (including Jonathan Rosenberg
when this document was originally discussed), Offer/Answer was always
intended to be asymmetrical. Each side can declare all the codecs it is
willing to receive and can send any codec remote party supports. I saw
multiple examples of this being implemented and used in exactly this manner.

In your example, if you need to free resources for H.264, you need to do
another Offer/Answer exchange in which you will send an offer with VP8 only.

Roman Shpount