mirrors/gstreamer
mirrors/gstreamer
1
1
Fork 0
mirror of https://gitlab.freedesktop.org/gstreamer/gstreamer.git synced 2024-07-10 00:25:53 +00:00
Code Issues 1 Projects Releases Wiki Activity

design/negotiation: fix structure and organization by sub-topic

Browse source
This commit is contained in:
Reynaldo H. Verdejo Pinochet 2016-12-19 11:49:57 -08:00
parent e276193d89
commit 90fab74103
1 changed files with 10 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

20
markdown/design/negotiation.md
View file

@ -21,7 +21,7 @@ There are 4 queries/events used in caps negotiation:
3) `GST_EVENT_CAPS`: configure format (downstream)
4) `GST_EVENT_RECONFIGURE`: inform upstream of possibly new caps
# Queries
## Queries
A pad can ask the peer pad for its supported GstCaps. It does this with
the CAPS query. The list of supported caps can be used to choose an
@ -57,7 +57,7 @@ GStreamer’s two scheduling modes, push mode and pull mode, lend
themselves to different mechanisms to achieve this goal. As it is more
common we describe push mode negotiation first.
## Push-mode negotiation
### Push-mode negotiation
Push-mode negotiation happens when elements want to push buffers and
need to decide on the format. This is called downstream negotiation
@ -135,7 +135,7 @@ One possible implementation in pseudo code:
endif
```
# Negotiate allocator/bufferpool with the ALLOCATION query
#### Negotiate allocator/bufferpool with the ALLOCATION query
buffer = gst_buffer_new_allocate (NULL, size, 0);
# fill buffer and push
@ -171,9 +171,9 @@ push buffer |---------------->| Process buffer of type B
| |
```
# Use case:
#### Use cases:
## `videotestsrc ! xvimagesink`
##### `videotestsrc ! xvimagesink`
* Who decides what format to use?
- src pad always decides, by convention. sinkpad can suggest a format
@ -201,7 +201,7 @@ push buffer |---------------->| Process buffer of type B
bufferpool. The sink will put the new new preferred format high in the list
of caps it returns from its caps query.
## `videotestsrc ! queue ! xvimagesink`
##### `videotestsrc ! queue ! xvimagesink`
- queue proxies all accept and caps queries to the other peer pad.
- queue proxies the bufferpool
@ -209,9 +209,9 @@ push buffer |---------------->| Process buffer of type B
- queue stores CAPS event in the queue. This means that the queue can
contain buffers with different types.
## Pull-mode negotiation
### Pull-mode negotiation
### Rationale
#### Rationale
A pipeline in pull mode has different negotiation needs than one
activated in push mode. Push mode is optimized for two use cases:
@ -277,7 +277,7 @@ happens.
The time to do capsnego, then, is after the SCHEDULING query has
succeeded, but before the sink has spawned the pulling thread.
### Mechanism
#### Mechanism
The sink determines that the upstream elements support pull based
scheduling by doing a SCHEDULING query.
@ -310,7 +310,7 @@ applications that expect ASYNC return values from sinks but it also
allows us to perform the remainder of the negotiation outside of the
context of the pulling thread.
## Patterns
### Patterns
We can identify 3 patterns in negotiation: