--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/gst_plugins_base/gst/playback/README Tue Aug 31 15:30:33 2010 +0300
@@ -0,0 +1,91 @@
+decodebin:
+
+ A bin with a sinkpad that decodes the data into raw formats. It works by sending
+ the input data through a typefind element and then recursively autoplugs elements
+ from the registry until a raw format is obtained. It will then create a new ghostpad
+ on itself to signal the app of the new pad.
+
+ Decodebin will also remove pads when they are removed from the stream.
+
+ TODO
+ - reuse of decoderbin, cleanup in READY state
+ - threading after demuxing?
+ - new_media events should be handled.
+ - caching of elements.
+ - abstract more elements, pads (typefind, ...);
+
+ The autoplugging happens as follows:
+
+ 1) typefind is added internally to the bin.
+ 2) the have_type signal is connected to typefind.
+ 3) in the have_type callback the close_pad_link function is called
+ 4) close_pad_link checks the type on the pad, if it is raw, a ghostpad
+ is created and autoplugging for that pad stops.
+ 5) if the type of the pad is not raw, a list of possible elements that
+ can connect to this type is generated in find_compatibles.
+ 6) try_to_link_1 with the element list is called. The function will loop
+ over the element list and will try to connect one of the elements to
+ the pad. If the link works, a call is made to close_link.
+ 7) close_link loops over all the source pads of the element and
+ recursively calls 4) for any ALWAYS pad. For elements with
+ a SOMETIMES pad, a structure is set up and is passed to the callback
+ of the new_pad signal.
+ 8) in the new_pad callback, 4) is called to try to autoplug the
+ new pad.
+
+
+playbasebin:
+
+ A bin with an uri property. It will find the right source element from the registry
+ and connect a decoderbin to it. When going to the PAUSED state, it will iterate the
+ decoderbin and listen for new pad signals from it. It will connect a queue to each
+ new pad and will iterate the decoderbin until one of the queues is filled. It is
+ assumed that by that time all the streams will be found so that when leaving the
+ PAUSED state, one can query the number of streams in the media file with the given
+ uri.
+
+ Playbasebin internally groups related streams together in a GstPlayBaseGroup. This
+ is particulary important for chained oggs. Initially, a new group is created in
+ the 'building' state. All new streams will be added to the building group until
+ no-more-pads is signaled or one of the preroll queues overflows. When this happens,
+ the group is commited to a list of groups ready for playback. PlaybaseBin will then
+ attach a padprobe to each stream to figure out when it finished. It will remove
+ the current group and install the next playable group, then.
+
+ Before going to the PLAYING state, it is possible to connect a custom element to
+ each of the streams. To do that, you have to add the element to the bin and then
+ connect the pad(s) from the stream(s). You do not have to add the elements in
+ a thread, the bin will take care of then when it's needed. You are allowed to use
+ threads inside the elements, of course.
+ The bin tries to be smart and doesn't add a queue when there is only one possible
+ stream.
+
+
+ TODO
+ - reuse, cleanup in ready state
+ - when the first pad is closed, it's possible that another dynamic element is
+ added somewhere so that we need a queue for the first pad as well.
+
+
+playbin:
+
+ Extends playbasebin, sets up default audiosink and videosink for first audio/video
+ stream detected. implements seeking and querying on the configured sinks.
+
+ It also waits for new notifications from playbasebin about any new groups that are
+ becomming active. It then disconnects the sinks and reconnects them to the new
+ pads in the group.
+
+ TODO
+ - reuse, refcounting, cleanup in READY state
+ - be smarter about replugging the sinks instead of removing them and readding them.
+ - Do not crap out when the audio device is in use.
+
+
+general
+
+ TODO
+ - playlist support. maybe use a playlist bin that streams the contents of the
+ playlist on a pad, interleaved with new_media events. Also add a tuner
+ interface while we're at it.
+