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design: Minor update of streams document

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* Fix indentation of lists and code extracts
* Add link to segment design doc

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-docs/-/merge_requests/89>
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Edward Hervey 2020-05-12 08:08:10 +02:00 committed by Edward Hervey
parent ad6b3130ee
commit ea25788fe1
1 changed files with 28 additions and 27 deletions
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55
markdown/additional/design/streams.md
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@ -3,27 +3,29 @@
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)
- events, including:
- `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.
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` event marks the end of the stream. No more buffers are to be processed
after the `EOS` event.
```
+-----+-------+ +-++-+ +-+ +---+
@ -35,7 +37,8 @@ more buffers are to be processed after the EOS event.
- marks the start of a stream; unlike the `SEGMENT` event, there
will be no `STREAM_START` event after flushing seeks.
2) **`SEGMENT`**, rate, start/stop, time
2) **`SEGMENT`**, rate, start/stop, time. (See also
[Segments](additional/design/segments.md))
- 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`.
@ -49,25 +52,22 @@ more buffers are to be processed after the EOS event.
- displayable buffers are between start/stop of the `SEGMENT` (S). Buffers
outside the segment range should be dropped or clipped.
- `running_time`:
- `running_time`: For each buffer, a monotonically increasing value that can
be used to synchronize against the clock (See also
[synchronisation](additional/design/synchronisation.md)).
```
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
```
``` c
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](additional/design/synchronisation.md)).
- `stream_time`: The current position in the stream, between 0 and duration.
- `stream_time`:
* current position in stream between 0 and duration.
```
stream_time = (B.timestamp - S.start) * ABS (S.applied_rate) + S.time
```
``` c
stream_time = (B.timestamp - S.start) * ABS (S.applied_rate) + S.time;
```
4) **`EOS`**
@ -75,6 +75,7 @@ more buffers are to be processed after the EOS event.
should refuse more data and return `GST_FLOW_EOS`. A `FLUSH_STOP`
event clears the `EOS` state of an element.
## Elements
These events are generated typically either by the `GstBaseSrc` class for