See also: IRC log
<trackbot> Date: 19 March 2013
<paulc> Good morning, Adrian (evening in Beijing)
<jon> zakim aabb is me
<adrianba> ScribeNick: adrianba
<scribe> Scribe: Adrian Bateman
paulc: this is a call of the
Media Task Force of the HTML WG
... focus on Media Source today - alternate every two
weeks
... ask for people to identify themselves
... objective to get through liaison questions and first
bugs
... to give them feedback on bugs
... hope editors ready for that - know there have been some
responses on individual bugs
... I'm Paul Cotton, from Microsoft, co-chair
adrianba: Adrian Bateman, Microsoft, Internet Explorer team
<Michael_Thornburgh> i'm from Adobe
[... members of the call identifying themselves]
<jon> I'm Jon Piesing from TP Vision, what used to be the TV business of Philips. I'm the chair of the browser group in OIPF and of the specification group in HbbTV.
<SimonW> Simon Waller from Samsung, I work on IP standardisation for TVs in OIPF and HbbTV
<Steve_Morris> I'm Steve Morris from Espial, working in both HbbTV and OIPF
<giuseppep> Giuseppe from Opera, working on Opera TV product. co-chair of the web&tv and also active in OIPF and HbbTV
<stevep> Stephen Perrott from the BBC in the UK. Here as part of the OIPF and DTG guest contingent.
paulc: that's done the introductions
<jbHenry> I'm J.B. Henry, from Orange group, working with HbbTV (and also OIPF)
<acolwell> Aaron Colwell from Google. I work on Chrome HTML5 video and I'm editor of the Media Source Extension spec.
<David_Corvoysier> I'm from Orange, both attending W3C HTML WG & Web &TV IG and OIPF
<guy> Guy Paskar, Peer5, Peer assisted delivery network utilizing MSE for creating the video from multiple sources.
paulc: first topic is the question from the liaison groups
<stephane> Stephane Lejeune and Alain Tholon with NDS in France working on HbbTV.
MSE questions from Open IPTV Forum, HbbTV and the UK DTG
<BobLund> Bob Lund from CableLabs working on browsers for TV, and DLNA and W3C related efforts.
<nsm> Nigel Moore - Sony Europe. Working on IPTV and web standards for CE devices in DTG, OIPF and HbbTV groups.
http://lists.w3.org/Archives/Public/public-html-media/2013Mar/0039.html
<ddorwin> David Dorwin from Google Chrome; co-editor of Encrypted Media Extensions.
<paulc> Response: http://lists.w3.org/Archives/Public/public-html-media/2013Mar/0048.html
<skaiser> Stefan Kaiser from Fraunhofer FOKUS, working on adaptive streaming / DASH applications
paulc: Q1. Are there plans for test cases for MSE?
acolwell: i was under the impression that the process requires this
paulc: process in W3C is specs go
through series of Working Drafts
... First WD has been published, typically publish new WD every
3 months
... when the WG is done, it approves going into Last Call, Last
Call Working Draft, and then look for public review
... once all comments are processed, spec moves to Candidate
Recommendation
... that transition requires WG approval and approval of W3C
Director
... at this stage there is a public call for
implementations
... usually need test cases to show interop and that spec is
clear enough for third party to implement from spec
... not unusual for there to be test cases before CR
... only at CR is mandatory
... is there a reason for the question?
jon: for the three organisations
a test suite is important
... we were not that familiar with w3c practice
... the only immediate question is one of timescales
... think we're done with this question
SimonW: i think this will be covered with schedule
paulc: Q2. Do you believe MSE contains the features needed for a DASH player that fully supports the DASH profiles defined by MPEG and by DASH-IF? If a DASH player on top of MSE could only support a subset of these profiles, is there any information on what could not be supported?
markw: for iso bmff i'm fairly
sure MSE can support a DASH player
... haven't done this for MPEG2-TS
acolwell: also my assessment
BobLund: we provided bitstream definition for MPEG2-TS and this was driven by requirements for DASH support
adrianba: appreciate specific bug reports if people think something is missing or broken
Q3. Has any thought gone into how MSE could be used with a media element whose playback rate was other than 0 or 1? Particularly rates greater than 1 or less than 0.
acolwell: two ways this could be
handled
... this should be signaled by setting rate on media element
just like the non MSE case
... either just append faster because media engine needs
faster
... or if you could use difference sourcebuffers for more
sophisticated output (e.g. key frame) and switch tracks with
html5
SimonW: what happens to the
timelines if you switch sourcebuffer and then you switch
back
... you want to switch into a different time
acolwell: my assumption, if
you're using a different buffer you're still using the real
timeline
... so it's really just track selection
... the current playback position is just moved forward
normally
... depending which sourcebuffer you're using you might only be
decoding keyframes
... but they're all the same timeline
<adrianba_> ScribeNick: adrianba_
paulc: Q4: Is there a complete description for the handling of encrypted content with an embedded DRM?
acolwell: this is covered by
EME
... there was care taken to make sure encryption cases were
handled but not called out
<paulc> EME = Encrypted Media Extensions
acolwell: because some people want to support MSE but not necessarily encryption
See http://lists.w3.org/Archives/Public/public-html-media/2013Mar/0048.html for example
<markw> yep, that's correct
johnsim: same for ISO
jon: that is the answer i was expecting
<adrianba> ScribeNick: adrianba
paulc: we've kept MSE and EME
separate but there are people planning to implement both
... Q5. The broadcasters in our 3 organisations have a
requirement to know when a particular advert starts being
played and stops being played so that they can report this
information back to an advertising server. It seems to us that
the (only?) way to achieve this with with MSE is to remember a)
where in the timeline the advert has been inserted (as defined
by timestampOffset) and b) the length of the advert. As the
content is played, the app wo
uld poll the currentTime property of the media element and test if this was within an advert. Is this how you ... would expect this requirement to be met with MSE?
acolwell: this is one way to do
it
... i would expect to use the existing html5 text track to do
this
... create text cues with the metadata
... for the start and end
... when the playback reaches those cues it will fire an
event
... without the need for polling
... could use inband tracks for this too
BobLund: here at cablelabs we've implemented both approaches and would be happy to provide details to anyone interested
paulc: thanks for the offer
paulc: may have been more bugs filed - there were 5 when i created the agenda
<paulc> https://www.w3.org/Bugs/Public/show_bug.cgi?id=21298
<BobLund> Contact b.lund@cablelabs.com for implementation details of using text tracks for advertisement audits
paulc: each bug has a history in it
Bug 21298 - making it easier for people to understand MSE
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21298
acolwell: the actionable piece
here was about creating a diagram
... about how appended data flows through the system
... open to more suggestions but this is for implementers so a
lot of prose makes it difficult to keep clear what is
normative
... could create a separate document for content owners
SimonW: helpful to have a high
level overview for how it all works together
... a separate document perhaps
... for example implementation guidelines for apps
paulc: not uncommon to produce a
primer in W3C
... for example XML Schema
... Part 0 is the primer and read more often than the normative
spec
... that model or introductary material in an annexe also
possible
jon: if you want good feedback need to reduce the learning curve
Bug 21299 - memory management in MSE
<paulc> https://www.w3.org/Bugs/Public/show_bug.cgi?id=21299
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21299
acolwell: this bug is around what
assumptions MSE is making about how memory is managed
... easiest way to think about this is SourceBuffers contain
trackbuffers
... which hold timeranges
... remove() allows removing ranges from the timeline
... only assumption is that you have these buffers of coded
frames and you can remove time ranges
... and encoding dependencies are taken into account
... don't believe any other assumptions about algorithms or
methods of storage
jon: this section was added after
our F2F
... two immediate things spring to mind
... does the app have to call remove()
acolwell: not required any more
for remove to be called
... we did have this requirement for a while but went back to
the original model
... intent is that if you don't call remove then UA will manage
buffer for you
... and attempt to ensure playback doesn't stall
... if app wants different algorithm then it can use
remove
... also heard that some apps have contractual obligations
about how much can be buffered
jon: that alleviates one concern
- would apps know enough to meaningfully call remove
... but if use case is limit for rights reason then that's
fine
acolwell: if app happens to know
something, for example if user executes a seek and knows won't
need old data then app could remove
... this might be info UA doesn't have
Bug 21300 - lack of clarity around appendStream
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21300
acolwell: MSE spec doesn't talk
about what creates Stream object
... MSE doesn't care but common use case is XHR
... XHR is XMLHttpRequest object
... primarily how apps that use MSE will fetch media data from
the media server
... using JavaScript to initiate HTTP requests
Bug 21301 - timelines in MSE and HTML5
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21301
acolwell: if we don't have questions, how do we close bugs?
paulc: want to answer these at
the end
... but if editors think they've answered the question, they
resolve the bugs
jon: the other option would be for the chairs to have an offline discussion
bug 21301
acolwell: this was a
clarification of terms - spec uses presentation timeline and
timeline without being defined
... so resolution is to use 'media timeline' which HTML5
uses
... trivial change
Bug 21302 - Support for inserting adverts as non-fragmented MP4 files
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21302
acolwell: my suggestion is not to
support this but i'm not sure how to attack this bug
... non-fragmented files do not follow the model of everything
else in the spec
... and while i understand current ad systems do not support
fragmented files i think they will
... adding this might cause legacy helpful in the short term
but not the long term
jdsmith: while it is technically
possible to make this work it is definitely a problem
... [some of the problems listed]
... our position is to not spend time on this
acolwell: seems like a business problem not a technical problem
jdsmith: tools are available to do this processing
jon: the reason you didn't get a
response is i don't think you have the advertising-funded
broadcasters here
... need to get them to think about this
<jon> Correction: The people who aren't here are the advertising-funded broadcasters.
acolwell: if it's not clear already i think you'll face strong pushback on supporting non-fragmented MP4
Bug 21333 - consequences of requirement in section 8 on initialisation segments
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21333
jon: typical example is you might
have a content item where there is one video track and the
audio track is multi-channel
... video might be the same codec but audio is different
... other example is content has multiple audio tracks but ad
doesn't
... this seemed to force us into different SourceBuffers
... what user experience would you get at the change between
SourceBuffers
adrianba: [summarises comments in the bug]
acolwell: channel count can be supported in a single sourcebuffer but codec change, as adrian says, for implementation reasons you don't usually support codec changes mid-presentation, especially for hardware decoding
<markw> I was going to agree this is a Media Element problem: what happens when you play a normal media file in which one audio track stops and another starts at some point in time ? Does the Media Element automatically switch tracks ?
acolwell: so using two
sourcebuffers to handle this would mean there is a track
change
... track changes are not considered seamless at this time
jon: this needs more
discussion
... if an audio track disappears that would seem to require a
sourcebuffer change
... we want something as seamless as possible
... for ad insertion
acolwell: that's not because of
the spec - the content you're using forces this
... because you're using content that can't be guaranteed to be
seamless
<jon> There's at least one more bug to come.
paulc: chairs are going to have
to continue our discussions
... ask editors to continue to close bugs as appropriate and
keep discussing others
... liaison guests - please let us know which need more
clarifications
... also would you like another meeting after a subsequent
meeting on your side
... mark as NEEDSINFO or whatever is appropriate
... i'll work with liaison chairs to make sure process is
understood
acolwell: should some questions
that are clarification be mails instead of bugs
... bugs are for things that need to be changed
... mails for discussion
paulc: yes, if there are questions that should be answered by reading spec, can start in the list
<giuseppep> can non HTML WG members give contributions to the group?
paulc: tend to encourage to use
bugs when can point to specific point in the spec and have a
proposal for changes
... will provide minutes to our partners
jon: like to express thanks for time and energy put into answering questions
paulc: adjourned, thanks
<jon> ?
<jon> quit
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