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

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Reynaldo H. Verdejo Pinochet 2016-12-19 11:49:57 -08:00
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markdown/design/negotiation.md
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@ -21,7 +21,7 @@ There are 4 queries/events used in caps negotiation:
3) `GST_EVENT_CAPS`: configure format (downstream) 3) `GST_EVENT_CAPS`: configure format (downstream)
4) `GST_EVENT_RECONFIGURE`: inform upstream of possibly new caps 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 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 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 themselves to different mechanisms to achieve this goal. As it is more
common we describe push mode negotiation first. common we describe push mode negotiation first.
## Push-mode negotiation ### Push-mode negotiation
Push-mode negotiation happens when elements want to push buffers and Push-mode negotiation happens when elements want to push buffers and
need to decide on the format. This is called downstream negotiation need to decide on the format. This is called downstream negotiation
@ -135,7 +135,7 @@ One possible implementation in pseudo code:
endif endif
``` ```
# Negotiate allocator/bufferpool with the ALLOCATION query #### Negotiate allocator/bufferpool with the ALLOCATION query
buffer = gst_buffer_new_allocate (NULL, size, 0); buffer = gst_buffer_new_allocate (NULL, size, 0);
# fill buffer and push # 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? * Who decides what format to use?
- src pad always decides, by convention. sinkpad can suggest a format - 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 bufferpool. The sink will put the new new preferred format high in the list
of caps it returns from its caps query. 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 all accept and caps queries to the other peer pad.
- queue proxies the bufferpool - 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 - queue stores CAPS event in the queue. This means that the queue can
contain buffers with different types. contain buffers with different types.
## Pull-mode negotiation ### Pull-mode negotiation
### Rationale #### Rationale
A pipeline in pull mode has different negotiation needs than one A pipeline in pull mode has different negotiation needs than one
activated in push mode. Push mode is optimized for two use cases: 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 The time to do capsnego, then, is after the SCHEDULING query has
succeeded, but before the sink has spawned the pulling thread. succeeded, but before the sink has spawned the pulling thread.
### Mechanism #### Mechanism
The sink determines that the upstream elements support pull based The sink determines that the upstream elements support pull based
scheduling by doing a SCHEDULING query. 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 allows us to perform the remainder of the negotiation outside of the
context of the pulling thread. context of the pulling thread.
## Patterns ### Patterns
We can identify 3 patterns in negotiation: We can identify 3 patterns in negotiation: