2.6 KiB
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
STREAM_START
(START)SEGMENT
(SEGMENT)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 stream start event that marks the start of the stream, followed by a segment event that marks the buffer timestamp range. After that buffers are sent one after the other. After the last buffer an EOS marks the end of the stream. No more buffers are to be processed after the EOS event.
+-----+-------+ +-++-+ +-+ +---+
|START|SEGMENT| |B||B| ... |B| |EOS|
+-----+-------+ +-++-+ +-+ +---+
-
STREAM_START
- marks the start of a stream; unlike the SEGMENT event, there will be no STREAM_START event after flushing seeks.
-
SEGMENT
, rate, start/stop, time- marks valid buffer timestamp range (start, stop)
- marks
stream_time
of buffers (time). This is the stream time of buffers with a timestamp of S.start. - marks playback rate (rate). This is the required playback rate.
- marks applied rate (
applied_rate
). This is the already applied playback rate. (See also trickmodes) - marks
running_time
of buffers. This is the time used to synchronize against the clock.
-
N buffers
-
displayable buffers are between start/stop of the
SEGMENT
(S). Buffers outside the segment range should be dropped or clipped. -
running_time
:
-
if (S.rate > 0.0)
running_time = (B.timestamp - S.start) / ABS (S.rate) + S.base
else
running_time = (S.stop - B.timestamp) / ABS (S.rate) + S.base
-
a monotonically increasing value that can be used to synchronize against the clock (See also synchronisation).
-
stream_time
:- current position in stream between 0 and duration.
stream_time = (B.timestamp - S.start) * ABS (S.applied_rate) + S.time
EOS
- marks the end of data, nothing is to be expected after
EOS
, elements should refuse more data and returnGST_FLOW_EOS
. AFLUSH_STOP
event clears theEOS
state of an element.
- marks the end of data, nothing is to be expected after
Elements
These events are generated typically either by the GstBaseSrc
class for
sources operating in push mode, or by a parser/demuxer operating in
pull-mode and pushing parsed/demuxed data downstream.