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192 lines
7.2 KiB
Text
192 lines
7.2 KiB
Text
0.11 status 1 jun 2011
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----------------------
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Hello again GStreamer hackers,
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Here's another status update from the 0.11 branch. This one is packed
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with new stuff because it really took too long between the last
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update, but well..
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Misc Core Changes
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-----------------
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The first set of big core change was done by über hacker Sebastian Dröge.
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He removed our special GST_BOILERPLATE macro. Because of some API strangeness
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we needed to do actions in the base_init method, which the GST_BOILERPLATE
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macro set up for us. The base_init concept is unfortunately not supported
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by almost all language bindings so we wanted to clean this up and use the
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regular G_DEFINE_TYPE macros. By inheriting metadata and pad templates
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from the parent, the GST_BOILERPLATE macro could be removed.
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Removal of gst_pad_alloc_buffer
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-------------------------------
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The next big change was the removal of gst_pad_alloc_buffer along with
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all the pad_alloc functions. The pad_alloc function were used to both
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implement allocation of buffers and notify upstream elements of new media
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formats. The functionality is replace by 3 new things: GstBufferPool (as
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noted in the previous status update), a new ALLOCATION query and a new
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RECONFIGURE event.
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The ALLOCATION query is used to query the downstream elements about the
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buffer properties they would like. These properties include the size,
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prefix and alignment of the memory. The downstream element can also propose
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a GstBufferPool. It is then the upstream element that decides how it
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will allocate buffers. This allows us, for example, to make the video
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decoders specify their required memory alignment to the videosink.
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Since new format suggestions are no longer piggybacked upstream with the
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allocation, something new was needed to notify upstream elements of a
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format change. It started with bringing in the new RENEGOTIATE event
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that Thiago Santos had been experimenting with in the 0.10 branch. The
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new event basically lets upstream elements know that new formats are
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possible somewhere downstream and it would make them renegotiate a new
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format before pushing a new buffer.
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New format changes can also happen when new elements are linked, so
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gst_pad_link() will also send this RENEGOTIATE event upstream. As it turns
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out, adding new elements could also signal the availability of a new
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bufferpool or different ALLOCATION properties. The RENEGOTIATE event was
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thus renamed to the more generic RECONFIGURE event.
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The most impressive result of these changes is that most of the
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complicated code in GstBaseTransform could simply be removed.
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Sticky Events
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-------------
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The idea for the sticky events comes from the observation that a lot of the
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serialized downstream events (SEGMENT, EOS, TAGS, ..) are really context
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for the buffers that follow. The design called for making these events
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sticky on the pads, meaning that they become a property of the pads
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they travel over.
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The result is that the current timing information (SEGMENT event) or the
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current stream medatadata (TAG event) that is handled by the pad are
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directly accessible by looking at the last event that traveled on the pad.
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By making the events stick on the pads, we can propagate them downstream
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automatically when new pads are linked. This should solve one of the
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biggest 0.10 problems when dealing with dynamic pipelines, the loss of
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events (mostly NEWSEGMENT events).
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It was then only natural to also make the CAPS event a sticky downstream
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serialized event. CAPS are indeed also context for the buffers that follow.
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The caps property was also removed from GstBuffer, making caps negotiation
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separate from the buffer dataflow again.
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GstSegment changes
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------------------
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For the sticky events to work with SEGMENT events, we needed to change
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the SEGMENT event so that it became selfcontained. The complicated segment
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accumulation logic of 0.10 was simply removed and replaced with pad offsets.
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It is now possible to tweak the timing of the data comming from a pad by
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using the pad offset property.
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GstCaps optimizations
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---------------------
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It doesn't look like we'll be able to implement GstCaps iterators to 0.11 so
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Sebastian was looking for other ways to improve caps performance. One of the
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low hanging fruits was to pass the complete GstCaps structure to the
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GstBaseTransform transform_caps method. This allows for better and smarter
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implementations of the function at the cost of marginally more complex code.
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Sebastian also added a filter caps parameter to the gst_pad_get_caps()
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function. This allows the caller to pass preferences and possible caps to
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the function. The result is that the pad can make much better negotiation
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decisions.
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Sebastian also optimized gst_caps_is_subset()in the 0.10 branch and ported
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the results to 0.11 as well.
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with the still planned caps simplifications later, these changes should
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substantially improve caps negotiation speed.
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Pad probes
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----------
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Quite a few iterations were needed to reimplement the pad blocking and pad
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probes. The new infrastructure allows you to add callbacks for the various
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stages in the data transfer on a pad.
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It's now possible to be notified when no data is going over a pad with the
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IDLE probe. This should also fix one of the big problems with implementing
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dynamic pipelines and the old pad blocking.
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Not all features that we want to add to the new probes are implemented yet
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but they can be added later without much trouble.
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Other gems
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----------
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A new SCHEDULING query was added to get more information about the upstream
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elements scheduling properties.
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Tim-Philipp Müller finally removed our dependency on libxml2. Back in the
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day, we used XML for serialization of objects and the registry. Object
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serialization had long been deprecated and the XML registry was replaced
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with a much faster binary registry.
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Tim also removed the unversioned gst-launch, gst-inspect and gst-typefind
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scripts. They were always confusing and annoying for packagers and users,
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it is just easier
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Edward Hervey spent some time keeping the unit tests working and making
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sure the API docs are up to data.
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GstIterator was made more binding friendly By Johan Dahlin and Sebastian.
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And what about the plugins..
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----------------------------
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As usual, all -base plugins are kept in sync with the core API updates and
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the new features. They are always a good place to see how the new API can
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be used and how to port things.
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What's next
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-----------
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Almost all of the features laid out in the GStreamer conference last year
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are now implemented. We also have quite a few new cool features that
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slipped in. Things are shaping up indeed.
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The last big missing piece is the redesign of the caps fields for raw audio
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and video. We plan to finish that in the next weeks.
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There are also a few smaller things we would like to do: use GstQuery
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for the various caps functions, do GstFlowReturn for the query/event
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functions, ...
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Meanwhile we start the stabilization phase and we will do a first prerelease
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of 0.11 this week to bring things to a wider audience. Now is the time to
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catch up and start porting your plugins to 0.11.
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There is still a lot of work to be done to port plugins to 0.11 before we
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can release 1.0. I ask everyone again (and especially maintainers) to help
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us porting plugins, it's really a lot of work!
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Have a nice hacking week,
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Wim
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