[foms] Text of ISO/IEC DIS 23001-6 Dynamic Adaptive Streaming over HTTP

Wed Feb 16 16:56:43 PST 2011

On Feb 16, 2011, at 4:14 PM, Silvia Pfeiffer wrote:

I agree - I think we need profiles of DASH - in particular a
restriction to just one mime type being used in a file that should go
into a @src attribute of <video>, <audio> or <source>. Also, we'd need
to make sure it works with the @media query attribute of <source>
elements, thus targets particular device features.

I think the requirement should be that it must be possible to determine whether a manifest can be played without loading the manifest.

What I most wonder about is, if such a DASH file was to be used in
place of a media resource in the @src attribute of a <video>, <audio>,
or <source> element, what will its mime type be? It would make life
easy if the mime type could just be the mime type of the resource that
it stands for, e.g. when all referenced files are webm, the mime type
of the manifest file should be video/webm. Unfortunately, it is
proposed to be video/vnd.mpeg.dash.mpd which doesn't help the browser
in deciding whether it will support the resource type therein. Maybe
we could create a profile and then have something like video/dash+webm
and video/dash+mp4 as mime types which is much more informative.

They defined a "profiles" parameter to this MIME type which can be used to say which profile or profiles the manifest is compliant to.

So, if someone defines a profile which goes as far as specifying mp4+H.264+aac (say) and someone else goes defines a profile which specifies WebM+VP8+Vorbis, then it is possible to specify which one a manifest is compliant to. Or indeed that it is compliant to both, meaning that it can be played so long as you support one profile or the other.

...Mark

Cheers,
Silvia.

On Wed, Feb 16, 2011 at 2:39 AM, Jeroen Wijering
<jeroen at longtailvideo.com<mailto:jeroen at longtailvideo.com>> wrote:
Hello all,

I wanted to forward a couple of updates on the WebTV workshop. They've been two interesting days, especially on the adaptive streaming / content security front.  We had a session on both adaptive streaming (focussing on DASH) and on content protection (focussing on PIFF). Sheets of the presentations done at both sessions can be downloaded here:

http://www.w3.org/2010/11/web-and-tv/agenda.html

On the DASH side, the spec has just been released. Silvia has forwarded a download link already (see below). In short, it's a flexible XML format that seems to support all required use cases (fragments, range-requests, manifest polling, etc). Outstanding issues are:

*) Licensing. What happens here is not entirely clear. At their presentation, Microsoft committed to make available any patents in this area they have under the MPEG RAND license. The W3C is still going after other contributors to the spec, to see if they want to take similar steps.
*) Profiling. Since the system is quite flexible, it is possible to define profiles for DASH. Profiles can contain both limitations to the XML elements / attributes and the format of media files referenced in the XML. A "basic ondemand" profile is defined; there'l probably be a "basic-live" profile as well.

I attached example DASH files that use WebM to define both an ondemand and live stream. The ondemand one uses range requests to pull both the Cues and fragments. The live one uses reloading of the manifest (like Apple does), a URL template (so a full fragment list is not needed) and separate codec setup segments (so they're not constantly duped - I understand setup in Vorbis is quite big). They should give a rough idea of how an ondemand or live stream can be defined with a DASH manifest.

On the content protection side, there was some talking about PIFF - Microsoft's encrypted, fragmented MP4 format. Interesting about this is the clear separation of encryption/decryption and the rights management layer. All presenters backed this approach. Perhaps this is interesting for open video / WebM as well, since encryption can be very useful for e.g. basic content protection (no DRM, just keys) or privacy reasons.  Any real standardization seems a bit further away though. There's been no detailed proposal on how this decryption / key signalling could work in HTML5 (cross-browser and cross-codec).

Steve Lhomme, JB Kempf and Mark Watson were also there; please chime in if I missed anything interesting.

Kind regards,

Jeroen

On Feb 13, 2011, at 1:02 PM, Silvia Pfeiffer wrote:

FYI: MPEG have released their draft DASH standard for adaptive HTTP streaming.
Plus there is a group forming in the W3C about Web & TV, which is also
interested in the topic and looking at DASH with lots of interest.
Cheers,
Silvia.

---------- Forwarded message ----------
From: Thomas Stockhammer <stockhammer at nomor.de<mailto:stockhammer at nomor.de>>
Date: Sat, Feb 12, 2011 at 6:14 AM
Subject: [W3C Web & TV] Text of ISO/IEC DIS 23001-6 Dynamic Adaptive
Streaming over HTTP
To: public-web-and-tv at w3.org<mailto:public-web-and-tv at w3.org>

Experts,
it was pleasure to meet you all.

I wanted to make you aware that the
Text of ISO/IEC DIS 23001-6 Dynamic Adaptive Streaming over HTTP
is now available here
http://mpeg.chiariglione.org/working_documents/mpeg-b/dash/dash-dis..zip
Note that this is a draft standard.
Best regards
Thomas

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