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f9f59df2ca
Original commit message from CVS: more notes
268 lines
12 KiB
Text
268 lines
12 KiB
Text
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Properties:
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"template_caps"
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The union of all possible caps that a pad might have in any
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condition. Is a class property, and doesn't change over the
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life of an object. Set by the element during class init.
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"internal_caps"
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The caps that the element will allow on a pad, given its current
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state and the external_caps of all the other pads of the element.
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Set by the element.
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"external_caps"
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The caps representing what the core will allow on a pad. This is
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a combination of the peer's allowed caps, and filtering caps, and
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any in-process negotiation restrictions. Set by the core.
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"negotiated_caps"
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The format that the element will use. Set by the core.
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"filter_caps"
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The caps intersected with everything else during negotiation. Set
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by the application.
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"negotiable"
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A boolean that indicates that the pad is ready to negotiate. Set
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by the element.
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Negotiation steps, from the element perspective:
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- During object initialization, an element must set template_caps
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and allowed_caps for each pad.
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- In response to changes in the internal state of the element or in
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the peer_allowed_caps of any other pad owned by the element, the
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element should update allowed_caps of a pad.
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- Pads are initially created with negotiable as FALSE. When an
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element wants to indicate that negotiation is allowable, it should
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set negotiable to TRUE.
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- In response to a negotiate signal, an element should copy the caps
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in "allowed_caps" to "negotiated_caps", and extract any information
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needed to handle the format. At this point, "allowed_caps" is
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guaranteed to be fixed.
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Negotiation steps, from the core perspective:
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<ds> I'd like to split it up into manageable "projects"
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<ds> hopefully some of which we can recruit others to do
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<Company> i'd like a decision about if we drop threads
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<ds> in what sense?
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<ds> threads being not required?
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<Company> threads being not part of the API
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<ds> or threads being not used
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<Company> so no thread safety considerations
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<ds> I would like threads to not be part of the API
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<ds> requiring apps/plugins to be written thread-safely is insane
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<Company> the question is this: If someone calls gst_element_set_state (element, state), does he have to marshal it into the correct thread himself or not?
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<ds> no
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<ds> reason being: we already have to deal with subthreads
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<ds> we == the core
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<Company> then you'll have a lot of problems
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<Company> i'd like to just drop subthreads and be done with it
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--> StyXman (~mdione@200.59.114.71) has joined #gstreamer
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<ds> and run everything in one thread?
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<Company> yes
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<Company> schedulers are free to use threads though
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<ds> this is obviously a retreat
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<Company> right
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<ds> but perhaps a strategic one
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<Company> otherwise you have to guarantee that you get no races
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<ds> I've seen this as a viable option for some time
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<Company> there's stuff that just does not work as is currently
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<ds> it always seemed difficult to convince other people that it's the right thing to do
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<ds> for example, wtay
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<Company> like setting xwindow ids, changing states or app-events
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<Company> like seeks
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<-- iain has quit ("leaving")
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<Company> all of this has the typical thread issues currently: it sometimes works and sometimes crashes the app
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<Company> and that's not acceptable to me
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<ds> let's do it
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<Company> if you look at my 0.10 code, I've tried to have GstObjects belong to a "context"
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<ds> this all fits into the idea that I think we should be a lot more like gtk architecturally
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<ds> for example, gtk doesn't have anything like caps negotiation, where elements call each other recursively
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<Company> and have functions ensure they're in the right context or otherwise marshal
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<Company> yes it does
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<ds> ?
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<Company> size requests and allocations
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<ds> but that's more like how I want it -- setting a property and firing a signal telling others that it's updated
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<ds> as i understand it
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<Company> though gtk has the bonus of being a tree which we don't have, we have a directed, maybe cyclic graph
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<Company> and for caps, the graph isn't even directed
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<Company> gtk is far too simple for gst
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<ds> true
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<Company> i can't even come up with an analogy to a video transcoder
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<ds> but we do some relatively simple stuff in a complicated way
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<-- StyXman (~mdione@200.59.114.71) has left #gstreamer
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<Company> like?
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<ds> caps negotiation
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<Company> that's not simple
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<ds> passing around the data should be
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<ds> was it you or thomasvs that wanted to split core headers into app headers and plugin headers?
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<Company> I definitely wanted that
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<Company> app/plugin/registry to be exact
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<ds> registry?
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<ds> for functions that access "internal" stuff?
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<Company> stuff an app normally doesn't touch
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<Company> so we can do something like declare the "app" stuff supported for a longer time
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<ds> oooh, good call
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<ds> I'm sold
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<Company> so, now that threads are gone, what are the biggies I want in 0.10?
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<Company> 1) non-blocking main-loop integrated processing
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<ds> that's rather important if you don't have threads :)
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<Company> right
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<Company> but it works in my gst-01.0 stuff already
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<Company> minus the elements that need to be ported of cause
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<Company> which aren't that many fortunately
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<Company> though some are hard (like gnomevfs), because they have no non-blocking API
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<ds> a subclass of GstElement that fires up a helper thread?
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<ds> (dirty, but it works)
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<Company> probably
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<ds> - autopluggers would be easier to write if there was a core method
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<ds> to do what plugidentities do.
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<Company> no clue how to implement that
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<ds> there's also a note about bins being more involved with negotiation
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<Company> that's the next biggie: 2) fix the negotiation process to allow good autoplugging
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<ds> that was something I thought about last time around
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<Company> bins?
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<ds> that sounds like something I'd work on
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<ds> GstBin
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<Company> the only reason bhins still exist for me is to group elements
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<ds> so that a bin subclass could override how its children are negotiated
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<ds> much like GtkBin, actually
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<ds> and allocation
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<Company> hum
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<Company> how do you solve that issue with links that are only partly inside the bin and partly inside another one?
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<ds> that would be up to the parent (grandparent?)
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<Company> so all links must be in the same toplevel bin?
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<ds> yes
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<ds> isn't that the case currently?
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<ds> probably not checked
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<Company> pfff
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<Company> currently you can do anything
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<ds> heh
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<ds> what about state changes?
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<Company> dunno
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<Company> it's not really important for me
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<Company> apart from the EOS stuff
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<ds> I'd like states to be split into "what state does the app want me to be in" and "what state am I in"
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<ds> with the latter being under control of the element
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<Company> yeah, that'd be nice
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<ds> that way, you don't have multiple people trying to control the state
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<Company> we definitely need to fix EOS
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<Company> i'm not sure how we should handle errors
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<ds> element errors?
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<Company> yeah, if we want to explicitly unset errors or not
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<Company> currently on error the element goes to paused
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<ds> it's easier with actual_state
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<Company> in theory i just set it to PLAYING again and continue?
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<ds> the actual_state goes to PAUSED and fires a signal
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<Company> dunno, maybe actual_state should go to ERROR
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<ds> yeah
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<Company> that'd require gst_element_unset_error though
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<ds> with actual_state, we can add states without thinking too hard
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<Company> but if you can just unset it, why not just do it and continue
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<ds> the app may want to be involved
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<ds> especially to get the error message
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<ds> do we want a separate api section for autopluggers?
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<Company> why would we want that?
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<ds> or make it part of registry
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<Company> maybe s/registry/internal/ or some other name
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<ds> because autopluggers may want to access internal information that we wouldn't expose to apps or plugins
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<ds> could you add gst/gstcompat.c to your arch repo?
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<Company> hm
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<Company> what internal info would an autoplugger need
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<ds> depends
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<ds> whatever replaces plugidentities
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<Company> a simple one (decoder) just needs caps and ranks
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<ds> I meant for negotiation information
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<Company> hm
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<Company> no, i don't want a seperate section for it
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<Company> just put it in "internal", "extended" or whatever
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<ds> ok
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<ds> do we want to plan for the app api to be ABI compatible past 0.10?
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<ds> er, that's silly
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<ds> er, kinda silly
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<Company> API compat
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<Company> you could achieve ABI compat if you expose all objects just as typedefs
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<Company> lemme reboot into linux so i can add gstcompat.c
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<Company> brb
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<-- Company has quit (Read error: 104 (Connection reset by peer))
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--> Company (~Company@pD95D53D9.dip.t-dialin.net) has joined #gstreamer
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--> ploum (~ploum@21-4.CampusNet.ucl.ac.be) has joined #gstreamer
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<-- marv has quit (Read error: 104 (Connection reset by peer))
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<ds> so do you still support caps registration?
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<-- ploum has quit (Client Quit)
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<ds> registering media types, fields, descriptions, and default fixate functions?
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<ds> and validation
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<Company> yes
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<Company> that's an important thing we need
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<Company> otherwise people mess up by either carelessly doing stuff wrong or not understanding what they're supposed to do
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<ds> whose responsibility is it to register these?
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<ds> libgstplugins?
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<ds> a plugin?
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<ds> do we want this info in the registry so that a plugin can automatically be loaded to provide registration for video/x-raw-rgb?
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<Company> haven't really thought about that part yet
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<ds> it's somewhat similar to typefind functions
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<Company> yeah
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--> ultrafunk (~pd@eth779.vic.adsl.internode.on.net) has joined #gstreamer
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<Company> i'd probably have a seperate Factory for caps info
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<Company> and have the system load them when you use the caps info stuff
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<ds> should caps info be manditory?
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<ds> have you synced your repo?
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<Company> i'm trying to, but some commit was interrupted last time...
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<ds> how does one sync a local repository to fd.o?
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<ds> rsync?
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<Company> tla archive-mirror
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<ds> ah
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<Company> see rhythmbox.org => developers for how it works
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<Company> and _never_ press ctrl-c in arch
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<-- Misirlou has quit (Remote closed the connection)
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--> Misirlou (~asdf@c-24-125-118-27.va.client2.attbi.com) has joined #gstreamer
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<ds> is there a reason why a pad might know (and set) allowed_caps, but not be ready to negotiate?
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<Company> i don't know a good one
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<ds> know a bad one?
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<Company> "arch-mirror: unable to acquire revision lock (internal error in archive-pfs.c(pfs_lock_revision))"
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<Company> stupidly ordered code
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<Company> no, don't know one
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<ds> here's a good question:
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<ds> should the core negotiate links in a pipeline that are negotiatable, even though some other links are not negotiatable?
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<ds> this ends up making us negotiate some things multiple times
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<ds> filesrc ! mad ! audioconvert ! audioscale ! osssink
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<Company> the core doesn't know if links are negotiable
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<ds> it will in the future :)
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<Company> sinesrc ! identity ! osssink
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<Company> how does it know if sinesrc ! identity is negotiable?
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<ds> because the allowed_caps on the two pads intersect
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--> marv (~ilovekimm@host-216-76-232-134.hsv.bellsouth.net) has joined #gstreamer
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<ds> I'm pretty sure that I don't want gst_pad_link() to return negotiation errors
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<ds> ever
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<Company> you can't avoid that
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<ds> I want to separate "linkable" from "negotiable"
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<Company> ah, gst_pad_link
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<ds> so you can link videotestsrc ! identity ! osssink
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<Company> i confused it with GstPadLink
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<Company> yeah, i was thinking about that, too
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<ds> vts ! osssink won't link, since the pad templates don't intersect
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<Company> http://web.ics.purdue.edu/~kuliniew/wp/archives/2004/08/07/error-handling/
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<Company> :)
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<ds> right now the vts ! id ! osssink pipeline fails to link
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<Company> yeah
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<Company> and goom ! xvimagesink only fails when xvimagesink is at least READY
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<Company> (assuming your xv can't do RGB)
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