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desing/bufferpool: mark subsections as such

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Reynaldo H. Verdejo Pinochet 2016-12-20 21:54:04 -08:00
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markdown/design/bufferpool.md
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@ -10,7 +10,7 @@ Together with the ALLOCATION query, elements can negotiate allocation
properties and bufferpools between themselves. This also allows elements properties and bufferpools between themselves. This also allows elements
to negotiate buffer metadata between themselves. to negotiate buffer metadata between themselves.
# Requirements ## Requirements
- Provide a GstBufferPool base class to help the efficient - Provide a GstBufferPool base class to help the efficient
implementation of a list of reusable GstBuffer objects. implementation of a list of reusable GstBuffer objects.
@ -36,7 +36,7 @@ important when a new element, that can provide a bufferpool, is
dynamically linked dynamically linked
downstream. downstream.
# GstBufferPool ## GstBufferPool
The bufferpool object manages a list of buffers with the same properties such The bufferpool object manages a list of buffers with the same properties such
as size, padding and alignment. as size, padding and alignment.
@ -54,7 +54,7 @@ free algorithms of the buffers from the pool. This should allow for
different allocation strategies such as using shared memory or hardware different allocation strategies such as using shared memory or hardware
mapped memory. mapped memory.
# Negotiation ## Negotiation
After a particular media format has been negotiated between two pads (using the After a particular media format has been negotiated between two pads (using the
CAPS event), they must agree on how to allocate buffers. CAPS event), they must agree on how to allocate buffers.
@ -76,7 +76,7 @@ the peer pad as usual.
The allocation query can also return an allocator object when the buffers are of The allocation query can also return an allocator object when the buffers are of
different sizes and can't be allocated from a pool. different sizes and can't be allocated from a pool.
# Allocation query ## Allocation query
The allocation query has the following fields: The allocation query has the following fields:
@ -147,7 +147,7 @@ with the metadata that contains metadata-specific options.
Some bufferpools have options to enable metadata on the buffers Some bufferpools have options to enable metadata on the buffers
allocated by the pool. allocated by the pool.
# Allocating from pool ## Allocating from pool
Buffers are allocated from the pool of a pad: Buffers are allocated from the pool of a pad:
@ -180,14 +180,14 @@ pool. This behaviour can be changed by specifying the
`GST_BUFFER_POOL_FLAG_DONTWAIT` flag in the parameters. With this flag set, `GST_BUFFER_POOL_FLAG_DONTWAIT` flag in the parameters. With this flag set,
allocation will return `GST_FLOW_EOS` when the pool is empty. allocation will return `GST_FLOW_EOS` when the pool is empty.
# Renegotiation ## Renegotiation
Renegotiation of the bufferpool might need to be performed when the Renegotiation of the bufferpool might need to be performed when the
configuration of the pool changes. Changes can be in the buffer size configuration of the pool changes. Changes can be in the buffer size
(because of a caps change), alignment or number of (because of a caps change), alignment or number of
buffers. buffers.
## Downstream ### Downstream
When the upstream element wants to negotiate a new format, it might need When the upstream element wants to negotiate a new format, it might need
to renegotiate a new bufferpool configuration with the downstream element. to renegotiate a new bufferpool configuration with the downstream element.
@ -205,7 +205,7 @@ The element that wants to renegotiate a new bufferpool uses exactly the same
algorithm as when it first started. It will negotiate caps first then use the algorithm as when it first started. It will negotiate caps first then use the
ALLOCATION query to get and configure the new pool. ALLOCATION query to get and configure the new pool.
## upstream ### upstream
When a downstream element wants to negotiate a new format, it will send a When a downstream element wants to negotiate a new format, it will send a
RECONFIGURE event upstream. This instructs upstream to renegotiate both RECONFIGURE event upstream. This instructs upstream to renegotiate both
@ -220,7 +220,7 @@ A RECONFIGURE event tags each pad it travels on as needing reconfiguration.
The next buffer allocation will then require the renegotiation or The next buffer allocation will then require the renegotiation or
reconfiguration of a pool. reconfiguration of a pool.
# Shutting down ## Shutting down
In push mode, a source pad is responsible for setting the pool to the In push mode, a source pad is responsible for setting the pool to the
inactive state when streaming stops. The inactive state will unblock any pending inactive state when streaming stops. The inactive state will unblock any pending
@ -232,9 +232,9 @@ shutting down so that the peer `_get_range()` function can unblock.
In the inactive state, all the buffers that are returned to the pool will In the inactive state, all the buffers that are returned to the pool will
automatically be freed by the pool and new allocations will fail. automatically be freed by the pool and new allocations will fail.
# Use cases ## Use cases
## - `videotestsrc ! xvimagesink` ### - `videotestsrc ! xvimagesink`
* Before videotestsrc can output a buffer, it needs to negotiate caps and * Before videotestsrc can output a buffer, it needs to negotiate caps and
a bufferpool with the downstream peer pad. a bufferpool with the downstream peer pad.
@ -271,7 +271,7 @@ the pool member.
this will cause further allocations to fail and currently allocated buffers to this will cause further allocations to fail and currently allocated buffers to
be freed. videotestsrc will then free the pool and stop streaming. be freed. videotestsrc will then free the pool and stop streaming.
## - ``videotestsrc ! queue ! myvideosink`` ### - ``videotestsrc ! queue ! myvideosink``
* In this second use case we have a videosink that can at most allocate 3 video * In this second use case we have a videosink that can at most allocate 3 video
buffers. buffers.
@ -307,7 +307,7 @@ bufferpool.
to inactive. This causes any pending (blocked) acquire to return with to inactive. This causes any pending (blocked) acquire to return with
a FLUSHING result and causes the streaming thread to pause. a FLUSHING result and causes the streaming thread to pause.
## - `.. ! myvideodecoder ! queue ! fakesink` ### - `.. ! myvideodecoder ! queue ! fakesink`
* In this case, the myvideodecoder requires buffers to be aligned to 128 bytes * In this case, the myvideodecoder requires buffers to be aligned to 128 bytes
and padded with 4096 bytes. The pipeline starts out with the decoder linked to and padded with 4096 bytes. The pipeline starts out with the decoder linked to
@ -334,7 +334,7 @@ the old bufferpool.
* The new bufferpool is set as the new bufferpool for the srcpad and sinkpad of * The new bufferpool is set as the new bufferpool for the srcpad and sinkpad of
the queue and set to the active state. the queue and set to the active state.
## - `.. ! myvideodecoder ! queue ! myvideosink ` ### - `.. ! myvideodecoder ! queue ! myvideosink `
* myvideodecoder has negotiated a bufferpool with the downstream myvideosink to * myvideodecoder has negotiated a bufferpool with the downstream myvideosink to
handle buffers of size 320x240. It has now detected a change in the video handle buffers of size 320x240. It has now detected a change in the video
@ -354,7 +354,7 @@ dimension.
can choose to use the current pool (which has buffers that are larger than the can choose to use the current pool (which has buffers that are larger than the
required size) or it can choose to renegotiate a new bufferpool. required size) or it can choose to renegotiate a new bufferpool.
## - `.. ! myvideodecoder ! videoscale ! myvideosink` ### - `.. ! myvideodecoder ! videoscale ! myvideosink`
* myvideosink is providing a bufferpool for upstream elements and wants to * myvideosink is providing a bufferpool for upstream elements and wants to
change the resolution. change the resolution.