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91 lines
4.1 KiB
Text
91 lines
4.1 KiB
Text
decodebin:
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A bin with a sinkpad that decodes the data into raw formats. It works by sending
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the input data through a typefind element and then recursively autoplugs elements
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from the registry until a raw format is obtained. It will then create a new ghostpad
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on itself to signal the app of the new pad.
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Decodebin will also remove pads when they are removed from the stream.
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TODO
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- reuse of decoderbin, cleanup in READY state
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- threading after demuxing?
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- new_media events should be handled.
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- caching of elements.
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- abstract more elements, pads (typefind, ...);
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The autoplugging happens as follows:
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1) typefind is added internally to the bin.
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2) the have_type signal is connected to typefind.
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3) in the have_type callback the close_pad_link function is called
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4) close_pad_link checks the type on the pad, if it is raw, a ghostpad
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is created and autoplugging for that pad stops.
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5) if the type of the pad is not raw, a list of possible elements that
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can connect to this type is generated in find_compatibles.
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6) try_to_link_1 with the element list is called. The function will loop
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over the element list and will try to connect one of the elements to
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the pad. If the link works, a call is made to close_link.
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7) close_link loops over all the source pads of the element and
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recursively calls 4) for any ALWAYS pad. For elements with
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a SOMETIMES pad, a structure is set up and is passed to the callback
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of the new_pad signal.
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8) in the new_pad callback, 4) is called to try to autoplug the
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new pad.
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playbasebin:
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A bin with an uri property. It will find the right source element from the registry
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and connect a decoderbin to it. When going to the PAUSED state, it will iterate the
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decoderbin and listen for new pad signals from it. It will connect a queue to each
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new pad and will iterate the decoderbin until one of the queues is filled. It is
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assumed that by that time all the streams will be found so that when leaving the
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PAUSED state, one can query the number of streams in the media file with the given
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uri.
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Playbasebin internally groups related streams together in a GstPlayBaseGroup. This
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is particulary important for chained oggs. Initially, a new group is created in
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the 'building' state. All new streams will be added to the building group until
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no-more-pads is signaled or one of the preroll queues overflows. When this happens,
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the group is committed to a list of groups ready for playback. PlaybaseBin will then
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attach a padprobe to each stream to figure out when it finished. It will remove
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the current group and install the next playable group, then.
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Before going to the PLAYING state, it is possible to connect a custom element to
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each of the streams. To do that, you have to add the element to the bin and then
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connect the pad(s) from the stream(s). You do not have to add the elements in
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a thread, the bin will take care of then when it's needed. You are allowed to use
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threads inside the elements, of course.
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The bin tries to be smart and doesn't add a queue when there is only one possible
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stream.
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TODO
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- reuse, cleanup in ready state
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- when the first pad is closed, it's possible that another dynamic element is
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added somewhere so that we need a queue for the first pad as well.
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playbin:
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Extends playbasebin, sets up default audiosink and videosink for first audio/video
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stream detected. implements seeking and querying on the configured sinks.
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It also waits for new notifications from playbasebin about any new groups that are
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becoming active. It then disconnects the sinks and reconnects them to the new
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pads in the group.
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TODO
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- reuse, refcounting, cleanup in READY state
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- be smarter about replugging the sinks instead of removing them and readding them.
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- Do not crap out when the audio device is in use.
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general
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TODO
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- playlist support. maybe use a playlist bin that streams the contents of the
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playlist on a pad, interleaved with new_media events. Also add a tuner
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interface while we're at it.
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