diff --git a/docs/design/part-bufferpool.txt b/docs/design/part-bufferpool.txt index 46b1a34b7e..743511f103 100644 --- a/docs/design/part-bufferpool.txt +++ b/docs/design/part-bufferpool.txt @@ -4,7 +4,7 @@ Bufferpool This document details the design of how buffers are be allocated and managed in pools. -Bufferpools increases performance by reducing allocation overhead and +Bufferpools increase performance by reducing allocation overhead and improving possibilities to implement zero-copy memory transfer. Together with the ALLOCATION query, elements can negotiate allocation properties @@ -40,7 +40,7 @@ GstBufferPool The bufferpool object manages a list of buffers with the same properties such as size, padding and alignment. - The bufferpool has two states: active and inactive. In the in-active + The bufferpool has two states: active and inactive. In the inactive state, the bufferpool can be configured with the required allocation preferences. In the active state, buffers can be retrieved from and returned to the pool. @@ -99,13 +99,13 @@ Allocation query guint max_buffers; } - use gst_query_parse_nth_allocation_pool() to get the values. + Use gst_query_parse_nth_allocation_pool() to get the values. The allocator can contain multiple pool configurations. If need-pool was TRUE, the pool member might contain a GstBufferPool when the downstream element can provide one. - Size contains the size of the bufferpool buffers and is never 0. + Size contains the size of the bufferpool's buffers and is never 0. min_buffers and max_buffers contain the suggested min and max amount of buffers that should be managed by the pool. @@ -125,7 +125,7 @@ Allocation query GstAllocationParams params; } - use gst_query_parse_nth_allocation_param() to get the values + Use gst_query_parse_nth_allocation_param() to get the values. The element performing the query can use the allocators and its parameters to allocate memory for the downstream element. @@ -144,7 +144,7 @@ Allocation query These metadata items can be accepted by the downstream element when placed on buffers. There is also an arbitrary GstStructure associated - with the metadata that contains metadata specific options. + with the metadata that contains metadata-specific options. Some bufferpools have options to enable metadata on the buffers allocated by the pool. @@ -214,7 +214,7 @@ of a caps change), alignment or number of buffers. RECONFIGURE event upstream. This instructs upstream to renegotiate both the format and the bufferpool when needed. - A pipeline reconfiguration is when new elements are added or removed from + A pipeline reconfiguration happens when new elements are added or removed from the pipeline or when the topology of the pipeline changes. Pipeline reconfiguration also triggers possible renegotiation of the bufferpool and caps. @@ -293,13 +293,13 @@ Use cases those elements require more than that amount of buffers for temporary storage. - The bufferpool of myvideosink will then be configured with the size of the + Myvideosink's bufferpool will then be configured with the size of the buffers for the negotiated format and according to the padding and alignment rules. When videotestsrc sets the pool to active, the 3 video buffers will be preallocated in the pool. videotestsrc acquires a buffer from the configured pool on its srcpad and - pushes this into the queue. When the videotestsrc has acquired and pushed + pushes this into the queue. When videotestsrc has acquired and pushed 3 frames, the next call to gst_buffer_pool_acquire_buffer() will block (assuming the GST_BUFFER_POOL_FLAG_DONTWAIT is not specified). @@ -324,9 +324,9 @@ Use cases decoder linked to a fakesink but we will then dynamically change the sink to one that can provide a bufferpool. - When it negotiates the size with the downstream element fakesink, it will + When myvideodecoder negotiates the size with the downstream fakesink element, it will receive a NULL bufferpool because fakesink does not provide a bufferpool. - It will then select its own custom bufferpool to start the datatransfer. + It will then select its own custom bufferpool to start the data transfer. At some point we block the queue srcpad, unlink the queue from the fakesink, link a new sink and set the new sink to the PLAYING state. @@ -334,7 +334,7 @@ Use cases and, through queue, inform myvideodecoder that it should renegotiate its bufferpool because downstream has been reconfigured. - Before pushing the next buffer, myvideodecoder would renegotiate a new + Before pushing the next buffer, myvideodecoder has to renegotiate a new bufferpool. To do this, it performs the usual bufferpool negotiation algorithm. If it can obtain and configure a new bufferpool from downstream, it sets its own (old) pool to inactive and unrefs it. This will eventually @@ -348,13 +348,13 @@ Use cases myvideodecoder has negotiated a bufferpool with the downstream myvideosink to handle buffers of size 320x240. It has now detected a change in the - video format and need to renegotiate to a resolution of 640x480. This - requires it to negotiate a new bufferpool with a larger buffersize. + video format and needs to renegotiate to a resolution of 640x480. This + requires it to negotiate a new bufferpool with a larger buffer size. When myvideodecoder needs to get the bigger buffer, it starts the negotiation of a new bufferpool. It queries a bufferpool from downstream, reconfigures it with the new configuration (which includes the bigger buffer - size) and it then sets the bufferpool to active. The old pool is inactivated + size) and sets the bufferpool to active. The old pool is inactivated and unreffed, which causes the old format to drain. It then uses the new bufferpool for allocating new buffers of the new @@ -371,7 +371,7 @@ Use cases change the resolution. myvideosink sends a RECONFIGURE event upstream to notify upstream that a - new format is desirable. upstream elements try to negotiate a new format + new format is desirable. Upstream elements try to negotiate a new format and bufferpool before pushing out a new buffer. The old bufferpools are drained in the regular way.