20:49:51 <RRSAgent> RRSAgent has joined #mediawg
20:49:51 <RRSAgent> logging to https://www.w3.org/2021/09/14-mediawg-irc
20:49:53 <Zakim> Zakim has joined #mediawg
20:50:07 <tidoust> Meeting: Media WG Teleconference
20:54:37 <MattWolenetz> MattWolenetz has joined #mediawg
20:58:22 <tidoust> Agenda: https://github.com/w3c/media-wg/blob/main/meetings/2021-09-14-Media_Working_Group_Teleconference-agenda.md
20:58:55 <MattWolenetz> present+ MattWolenetz
20:59:36 <tidoust> present+ Francois_Daoust, Bernard_Aboba, Joey_Parrish
20:59:44 <tidoust> RRSAgent, make logs public
21:00:59 <gregwf> gregwf has joined #mediawg
21:02:08 <tidoust> present+ Cyril_Concolato, Peng_Liu
21:02:09 <cyril> cyril has joined #mediawg
21:02:40 <pengliu> pengliu has joined #mediawg
21:03:09 <zacharycava> zacharycava has joined #mediawg
21:03:21 <tidoust> present+ Jer_Noble, Gary_Katsevman, Zachary_Cava, Chris_Cunningham, Greg_Freedman
21:04:03 <chcunningham> chcunningham has joined #mediawg
21:04:16 <cyril> present+ Cyril_Concolato
21:04:21 <tidoust> scribe: chcunningham
21:04:36 <jernoble> jernoble has joined #mediawg
21:04:45 <chcunningham> present+ Chris Cunningham
21:04:50 <jernoble> present+ jernoble
21:05:03 <tidoust> present+ Chris_Needham
21:05:04 <gkatsev> present+ Gary_Katsevman
21:05:40 <chcunningham> cpn: focus of today MSE issues
21:06:23 <chcunningham> ... first AOB item: TPAC
21:06:28 <tidoust> present+ Jan-Ivar_Bruaroey
21:06:37 <tidoust> present+ Eric_Carlson
21:06:43 <chcunningham> ... media ig planning meetings to assess future direction of web tech for consumer devices
21:06:58 <chcunningham> ... in collab w/ cta wav and others
21:07:14 <chcunningham> ... date: 25 October, more details coming soon
21:07:34 <chcunningham> ... WG members invited to join
21:07:39 <tidoust> s/cta wav/CTA WAVE/
21:08:10 <chcunningham> aboba: Also joint meeting w/ WebRTC group
21:08:48 <chcunningham> ... on 26 October
21:08:53 <cpn> https://www.w3.org/wiki/TPAC/2021/GroupMeetings
21:09:29 <chcunningham> cpn: today's focus, MSE issues
21:09:39 <chcunningham> ... thank you for cfc replies
21:09:48 <chcunningham> ... resolved: MSE in workers is ready to integrate
21:09:52 <tidoust> i/cpn: today's focus/Topic: Media Source Extensions
21:10:33 <tidoust> i/cpn: focus of today/Topic: A couple of media-related joint meetings during TPAC
21:10:49 <chcunningham> wolenetz: First issue, #184
21:10:56 <chcunningham> ... MSE for WebCodecs
21:11:21 <cpn> https://github.com/wolenetz/mse-for-webcodecs/blob/main/explainer.md <- Explainer
21:11:32 <tidoust> i/wolenetz: First issue/Subtopic: MSE for WebCodecs (#184)
21:11:43 <chcunningham> ... looking for authors to try origin trial, and feedback on API
21:11:58 <chcunningham> ... first promise-based MSE API
21:13:01 <chcunningham> ... summary: MSE would take WebCodecs chunks rather than containerized bytestreams
21:13:31 <chcunningham> ... expecting interest from player libraries, hls.js, etc, who could use this to avoid re-muxing
21:14:11 <tidoust> Subtopic: MSE-in-Workers: {Audio,Video,Text}Track{,List} IDL in HTML need additional DedicatedWorker in Exposed (#28
21:14:11 <tidoust> 0
21:14:11 <tidoust> )
21:14:33 <tidoust> RRSAgent, draft minutes
21:14:33 <RRSAgent> I have made the request to generate https://www.w3.org/2021/09/14-mediawg-minutes.html tidoust
21:14:46 <chcunningham> ... 280 how to expose HTMLMediaElement tracks in worker.
21:15:01 <chcunningham> ... currently, tracks interfaces exposed only in Window
21:15:02 <tidoust> s/)//
21:15:23 <chcunningham> ... 1) do we need tracks in worker?
21:15:27 <cpn> q?
21:15:28 <tidoust> s/(#28/(#280)
21:15:30 <chcunningham> ... 2) if yes, how to update html5 to go about it
21:16:05 <chcunningham> cpn: changes to html should go to whatwg
21:16:24 <chcunningham> ... question: tracks exist both on HTMLMediaElement and SourceBuffer. What's the difference?
21:16:53 <chcunningham> wolenetz: w/ SourceBuffer API, you can ask SB what tracks it specifically provides
21:17:03 <tidoust> s/... 280 how to/wolenetz: 280 how to
21:17:39 <chcunningham> ... note: currently Chromium doesn't expose tracks even in Window
21:18:38 <chcunningham> jer: Generally, I prefer MSE in worker to be as close to on main thread as possible. To facilitate easier adoption
21:20:10 <chcunningham> ... Probably not a big issue for HTML to expose tracks in Workers
21:20:33 <cpn> https://github.com/w3c/media-source/issues/277
21:20:38 <chcunningham> Subtopic: Threading lifetimes
21:21:56 <chcunningham> wolenetz: what happens to <video> when worker is terminated
21:22:20 <chcunningham> ... do we remove the buffers from <video> that MSE-in-worker was contributing?
21:22:38 <chcunningham> ... or do we let <video> retain what was buffered
21:23:15 <chcunningham> ... also, should <video> get some notification that worker termination occurred
21:24:12 <chcunningham> ... currently, chrome's mse-in-workers drops buffers after worker dies, but not sure if it's right
21:24:49 <chcunningham> jernoble: I would behave as if source object is removed from <video>. return to empty network state
21:25:15 <chcunningham> wolenetz: or potentially trigger EOS behavior?
21:25:57 <chcunningham> jernoble: that sounds more complicated. if source object disappears, most transparent thing is to remove the buffers
21:26:13 <chcunningham> ... could be detected by network state event
21:27:04 <chcunningham> ... similar to how <video> behaves w/ src set to empty string
21:27:32 <chcunningham> cyrl: can things be downloaded, buffered, then wasted if worker dies?
21:27:40 <chcunningham> s/cyrl/cyril/
21:28:14 <chcunningham> wolenetz: yes that could occur, but generally we expect the app to be driving the termination, so just a question about the short period of time following that
21:28:54 <chcunningham> cyril: fine to remove buffers if it's just for a short period.
21:29:42 <chcunningham> jernoble: "terminating" the worker would be caused by explicit terminate(), which in theory is only done by the client of the worker
21:30:16 <chcunningham> cyril: can the app wait to terminate until it's used all the buffer
21:30:19 <chcunningham> wolenetz: yes
21:31:24 <chcunningham> cpn: what do we need to spec from interop pov
21:32:05 <chcunningham> wolenetz: I like Jer's suggestion to detach as much as possible.
21:32:47 <chcunningham> cpn: can you reuse media element by setting a new src / srcObject?
21:32:51 <chcunningham> wolenetz: yes
21:33:42 <cpn> https://github.com/w3c/media-source/issues/275
21:34:25 <chcunningham> Subtopic: timing of initial HAVE_METADATA transition
21:35:19 <chcunningham> ... currently, HAVE_METADATA is spec'ed to be fired synchronously w/ arrival of init segment
21:35:53 <chcunningham> ... not feasible with workers. any concerns to relax it to be async
21:36:56 <chcunningham> ... specifically, bottom of init segment received algorithm: when all SB's have init segment received = true
21:37:17 <chcunningham> ... set's readyState = HAVE_METADATA
21:37:56 <chcunningham> jernoble: I think the time where init segment is processed is probably already arbitrary
21:38:49 <chcunningham> wolenetz: so it's probably ok to do async here as well? not blocking the worker on synchronously setting readyState?
21:38:58 <chcunningham> jernoble: I agree
21:40:12 <chcunningham> janivar: might be good to gather data on current browser behavior
21:40:19 <chcunningham> wolenetz: will do
21:40:49 <chcunningham> jernoble: do we have a wpt test for this? could use that to track differences
21:41:30 <chcunningham> wolenetz: test exists, but it's flaky
21:41:59 <chcunningham> jernoble: for webkit, we issue have_metadata before updated event
21:42:32 <cpn> https://github.com/w3c/media-source/issues/156
21:42:56 <chcunningham> Subtopic: Object URLs vs srcObject
21:43:18 <chcunningham> wolenetz: chromium regrettably doesn't support srcObject yet
21:44:10 <chcunningham> ... the original object URL was "autorevoking"
21:45:00 <chcunningham> ... Chrome changed behavior to let apps explicitly revoke to improve GC ability to collect
21:46:05 <chcunningham> ... for MSE-in-workers, we need to keep object URLs alive long enough to be used by worker (can't immediately revoke).
21:46:47 <chcunningham> ... proposal: for workers, what if we don't revoke until after first use.
21:47:51 <chcunningham> jernoble: I initially favored keeping the URL, but now I like srcObject. Still, usage of srcObject is very low because of missing support in other UAs
21:49:29 <chcunningham> wolenetz: we haven't decided how src would work w/ MSE-in-workers yet. so far just looked at using srcObject
21:50:16 <chcunningham> jernoble: for src url, we could maintain autorevoking behavior on the main thread while behaving differently for use in workers
21:50:42 <cpn> https://github.com/w3c/media-source/issues/28
21:51:54 <chcunningham> janivar: I'm supportive of srcObject. Firefox hasn't implemented it yet.
21:56:24 <chcunningham> jernoble: it seems simpler to create object in worker, do attachment on main thread, and have spec language say <video> informs the MSE-in-worker that they're now attached
21:56:54 <chcunningham> ... vs earlier proposals that considered creating src url in main thread
21:57:40 <chcunningham> janivar: beware, as you "transfer" objects, the typical language is that the source-side is "detached"
21:57:44 <chcunningham> q+
21:58:43 <chcunningham> wolenetz: Up next I'll be addressed Mark Watsons PR comments and taking a look at specter mitigations
21:59:06 <chcunningham> cpn: to confirm, for workers, we've aligned on srcObject for attachment?
21:59:11 <chcunningham> wolenetz: correct
21:59:54 <chcunningham> jernoble: something to consider, should <source> elements have srcObject attribute?
22:00:13 <chcunningham> Topic: next meeting
22:00:31 <chcunningham> cpn: scheduled for end of october. do we need anything sooner?
22:00:49 <chcunningham> cyril: I'd like an earlier session to discuss bytestream issues
22:01:26 <chcunningham> jer: how about same time in two weeks?
22:01:33 <chcunningham> q-
22:02:55 <chcunningham> cyril: in the meantime, please add your thoughts to the GH issues
22:04:02 <tidoust> RRSAgent, draft minuntes
22:04:02 <RRSAgent> I'm logging. I don't understand 'draft minuntes', tidoust.  Try /msg RRSAgent help
22:04:07 <tidoust> RRSAgent, draft minutes
22:04:07 <RRSAgent> I have made the request to generate https://www.w3.org/2021/09/14-mediawg-minutes.html tidoust
22:04:30 <MattWolenetz> s/specter/Spectre/
22:06:40 <tidoust> Chair: Chris, Jer
22:06:44 <tidoust> RRSAgent, draft minutes
22:06:44 <RRSAgent> I have made the request to generate https://www.w3.org/2021/09/14-mediawg-minutes.html tidoust