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docs: Gram and nit fixes for part-caps.txt

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Reynaldo H. Verdejo Pinochet 2013-10-14 18:05:43 -07:00
parent 72edc18465
commit 3d693f387f
1 changed files with 23 additions and 23 deletions
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46
docs/design/part-caps.txt
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@ -1,8 +1,8 @@
Caps Caps
---- ----
Caps are lighweight refcounted objects describing media types. Caps are lightweight refcounted objects describing media types.
They are composed of an array of GstStructures plus optionally They are composed of an array of GstStructures plus, optionally,
a GstCapsFeatures set for the GstStructure. a GstCapsFeatures set for the GstStructure.
Caps are exposed on GstPadTemplates to describe all possible types a Caps are exposed on GstPadTemplates to describe all possible types a
@ -23,22 +23,21 @@ Fixating
-------- --------
Caps are fixed if they only contain a single structure and this Caps are fixed if they only contain a single structure and this
structure is fixed. A structure is fixed if none of the fields of the structure is fixed. A structure is fixed if none of the fields of the
structure is a unfixed types, for example a range, list or array. structure is an unfixed type, for example a range, list or array.
For fixating caps only the first structure is kept as the order of For fixating caps only the first structure is kept as the order of
structures is meant to express the preferences for the different structures is meant to express the preferences for the different
structures. structures. Afterwards, each unfixed field of this structure is set
Afterwards each unfixed field of this structure is set to a value to the value that makes most sense for the media format by the element
that makes most sense for the media format by the element or pad or pad implementation and then every remaining unfixed fields are set to
implementation and afterwards every remaining unfixed fields is set to an arbitrary value that is a subset of the unfixed field possible values.
an arbitrary value that would be a subset of the unfixed field value.
EMPTY caps are fixed caps, ANY caps are not fixed. Caps with ANY caps EMPTY caps are fixed caps and ANY caps are not. Caps with ANY caps features
features are not fixed. are not fixed.
Subset Subset
------ ------
One caps "A" is the subset of another caps "B" if for each structure in One caps "A" is a subset of another caps "B" if for each structure in
"A" there exists a structure in "B" that is a superset of the structure "A" there exists a structure in "B" that is a superset of the structure
in "A". in "A".
@ -47,7 +46,7 @@ structure name, the same caps features and each field in "b" exists
in "a" and the value of the field in "a" is a subset of the value of in "a" and the value of the field in "a" is a subset of the value of
the field in "b". "a" can have additional fields that are not in "b". the field in "b". "a" can have additional fields that are not in "b".
EMPTY caps are a subset of every other caps, every caps are a subset of EMPTY caps are a subset of every other caps. Every caps are a subset of
ANY caps. ANY caps.
Equality Equality
@ -69,8 +68,8 @@ If one structure contains a field that is not existing in the other
structure it will be copied over to the intersection with the same structure it will be copied over to the intersection with the same
value. value.
The intersection with ANY caps is always the other caps, the The intersection with ANY caps is always the other caps and the intersection
intersection with EMPTY caps is always EMPTY. with EMPTY caps is always EMPTY.
Union Union
----- -----
@ -78,12 +77,12 @@ The union of caps "A" and caps "B" are the caps that contain the union
of all their structures with each other. of all their structures with each other.
The union of structure "a" and structure "b" are the two structures "a" The union of structure "a" and structure "b" are the two structures "a"
and "b" if the structure names or caps features are not equal. Otherwise and "b" if the structure names or caps features are not equal. Otherwise,
the union is the structure that contains the union of each fields value. the union is the structure that contains the union of each fields value.
If a field is only in one of the two structures it is not contained in If a field is only in one of the two structures it is not contained in
the union. the union.
The union with ANY caps is always ANY, the union with EMPTY caps is The union with ANY caps is always ANY and the union with EMPTY caps is
always the other caps. always the other caps.
Subtraction Subtraction
@ -108,13 +107,13 @@ Each of these structures has a name that specifies the media type, e.g.
structure add additional constraints and/or information about the media structure add additional constraints and/or information about the media
type, like the width and height of a video frame, or the codec profile type, like the width and height of a video frame, or the codec profile
that is used. These fields can be non-fixed (e.g. ranges) for non-fixed that is used. These fields can be non-fixed (e.g. ranges) for non-fixed
caps but must be fixed to a fixed value during negotiation. caps but must be fixated to a fixed value during negotiation.
If a field is included in the caps returned by a pad via the CAPS query, If a field is included in the caps returned by a pad via the CAPS query,
it imposes an additional constraint during negotiation. The caps in the it imposes an additional constraint during negotiation. The caps in the
end must have this field with a value that is a subset of the non-fixed end must have this field with a value that is a subset of the non-fixed
value. Additional fields that are added in the negotiated caps give value. Additional fields that are added in the negotiated caps give
additional information about the media but are treated as optional. additional information about the media but are treated as optional.
Information that can change for every buffer and are not relevant during Information that can change for every buffer and is not relevant during
negotiation must not be stored inside the caps. negotiation must not be stored inside the caps.
@ -124,9 +123,9 @@ for a specific structure, and only structures with the same name _and_
equal caps features are considered compatible. equal caps features are considered compatible.
Caps features can be used to require a specific memory representation Caps features can be used to require a specific memory representation
or a specific meta to be set on buffers, for example a pad could require or a specific meta to be set on buffers, for example a pad could require
for a specific structure that it is passed EGLImage memory or buffers for a specific structure that includes EGLImage memory or buffers with
with the video meta. the video meta.
If not caps features are provided for a structure, it is assumed that If no caps features are provided for a structure, it is assumed that
system memory is required unless later negotiation steps (e.g. the system memory is required unless later negotiation steps (e.g. the
ALLOCATION query) detect that something else can be used. The special ALLOCATION query) detect that something else can be used. The special
ANY caps features can be used to specify that any caps feature would ANY caps features can be used to specify that any caps feature would
@ -143,6 +142,7 @@ not enough. Instead the fixed caps must be at least a subset of the
pad's caps but pads can introduce additional constraints which would be pad's caps but pads can introduce additional constraints which would be
checked in the ACCEPT_CAPS query handler. checked in the ACCEPT_CAPS query handler.
Data flow can only happen after pads have decided on a common, fixed Data flow can only happen after pads have decided on a common and fixed
caps and these caps are distributed to both pads with the CAPS event. set of caps. These caps are then distributed to both pads with the CAPS
event.