gstreamer/gst/playback

decoderbin:

  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. 

  TODO
   - reuse of decoderbin, cleanup in READY state
   - debugging 
   - threading after demuxing?
   - better factory selection, based on Demuxer/Decoder types and ranks.
   - error handling

baseplaybin:

  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.
  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
  - debugging
  - 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.
  - error handling

playbin:
  
   Extends baseplaybin, sets up default audiosink and videosink for first audio/video
   stream detected. implements seeking and querying on the configured sinks.

   TODO
   - reuse, refcounting, cleanup in READY state
   - debugging
   - error handling