gstreamer/docs/design/part-streams.txt

Streams
-------

  This document describes the objects that are passed from element to
  element in the streaming thread.


Stream objects
--------------

The following objects are to be expected in the streaming thread:

 - events
    - NEW_SEGMENT	(NS)
    - EOS		(EOS)  *
    - TAG               (T)
 - buffers              (B)    *

Objects marked with * need to be synchronised to the clock in sinks
and live sources.


Typical stream
--------------

 A typical stream starts with a newsegment event that marks the
 buffer timestamp range. After that buffers are send one after the
 other. After the last buffer an EOS marks the end of the stream. No
 more buffer are to be processed after the EOS event.

  +--+ +-++-+     +-+ +---+
  |NS| |B||B| ... |B| |EOS|
  +--+ +-++-+     +-+ +---+

  1) NEW_SEGMENT, rate, start/stop, time
     - marks valid buffer timestamp range (start, stop)
     - marks stream_time of buffers (time)
     - marks playback rate (rate)

  2) N buffers
     - displayable buffers are between start/stop of the NEW_SEGMENT

     - display_time: (B.timestamp - NS.start) * NS.abs_rate
        * used to calculate stream_time and sync_time

     - stream_time:  display_time + NS.time
        * current position in stream between 0 and duration

     - sync_time:    display_time + NS.accum + base_time 
        * used to synchronize against the clock.

  3) EOS
     - marks the end of data, nothing is to be expected after EOS