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doc: update filter_design.txt to API changes.

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Nicolas George 12 years ago
parent cdc48860a8
commit 23686c72e5
1 changed files with 39 additions and 43 deletions
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  1. 82
      doc/filter_design.txt

82
doc/filter_design.txt
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@ -15,13 +15,13 @@ Format negotiation
the list of supported formats.
For video links, that means pixel format. For audio links, that means
channel layout, and sample format (the sample packing is implied by the
sample format).
channel layout, sample format (the sample packing is implied by the sample
format) and sample rate.
The lists are not just lists, they are references to shared objects. When
the negotiation mechanism computes the intersection of the formats
supported at each ends of a link, all references to both lists are
replaced with a reference to the intersection. And when a single format is
supported at each end of a link, all references to both lists are replaced
with a reference to the intersection. And when a single format is
eventually chosen for a link amongst the remaining list, again, all
references to the list are updated.
@ -68,15 +68,15 @@ Buffer references ownership and permissions
Here are the (fairly obvious) rules for reference ownership:
* A reference received by the start_frame or filter_frame method
belong to the corresponding filter.
* A reference received by the filter_frame method (or its start_frame
deprecated version) belongs to the corresponding filter.
Special exception: for video references: the reference may be used
internally for automatic copying and must not be destroyed before
end_frame; it can be given away to ff_start_frame.
* A reference passed to ff_start_frame or ff_filter_frame is given
away and must no longer be used.
* A reference passed to ff_filter_frame (or the deprecated
ff_start_frame) is given away and must no longer be used.
* A reference created with avfilter_ref_buffer belongs to the code that
created it.
@ -90,27 +90,11 @@ Buffer references ownership and permissions
Link reference fields
---------------------
The AVFilterLink structure has a few AVFilterBufferRef fields. Here are
the rules to handle them:
* cur_buf is set before the start_frame and filter_frame methods to
the same reference given as argument to the methods and belongs to the
destination filter of the link. If it has not been cleared after
end_frame or filter_frame, libavfilter will automatically destroy
the reference; therefore, any filter that needs to keep the reference
for longer must set cur_buf to NULL.
* out_buf belongs to the source filter of the link and can be used to
store a reference to the buffer that has been sent to the destination.
If it is not NULL after end_frame or filter_frame, libavfilter will
automatically destroy the reference.
If a video input pad does not have a start_frame method, the default
method will request a buffer on the first output of the filter, store
the reference in out_buf and push a second reference to the output.
* src_buf, cur_buf_copy and partial_buf are used by libavfilter
internally and must not be accessed by filters.
The AVFilterLink structure has a few AVFilterBufferRef fields. The
cur_buf and out_buf were used with the deprecated
start_frame/draw_slice/end_frame API and should no longer be used.
src_buf, cur_buf_copy and partial_buf are used by libavfilter internally
and must not be accessed by filters.
Reference permissions
---------------------
@ -119,8 +103,10 @@ Buffer references ownership and permissions
the code that owns the reference is allowed to do to the buffer data.
Different references for the same buffer can have different permissions.
For video filters, the permissions only apply to the parts of the buffer
that have already been covered by the draw_slice method.
For video filters that implement the deprecated
start_frame/draw_slice/end_frame API, the permissions only apply to the
parts of the buffer that have already been covered by the draw_slice
method.
The value is a binary OR of the following constants:
@ -179,9 +165,9 @@ Buffer references ownership and permissions
with the WRITE permission.
* Filters that intend to keep a reference after the filtering process
is finished (after end_frame or filter_frame returns) must have the
PRESERVE permission on it and remove the WRITE permission if they
create a new reference to give it away.
is finished (after filter_frame returns) must have the PRESERVE
permission on it and remove the WRITE permission if they create a new
reference to give it away.
* Filters that intend to modify a reference they have kept after the end
of the filtering process need the REUSE2 permission and must remove
@ -198,11 +184,11 @@ Frame scheduling
Simple filters that output one frame for each input frame should not have
to worry about it.
start_frame / filter_frame
----------------------------
filter_frame
------------
These methods are called when a frame is pushed to the filter's input.
They can be called at any time except in a reentrant way.
This method is called when a frame is pushed to the filter's input. It
can be called at any time except in a reentrant way.
If the input frame is enough to produce output, then the filter should
push the output frames on the output link immediately.
@ -213,7 +199,7 @@ Frame scheduling
filter; these buffered frames must be flushed immediately if a new input
produces new output.
(Example: framerate-doubling filter: start_frame must (1) flush the
(Example: framerate-doubling filter: filter_frame must (1) flush the
second copy of the previous frame, if it is still there, (2) push the
first copy of the incoming frame, (3) keep the second copy for later.)
@ -233,8 +219,8 @@ Frame scheduling
This method is called when a frame is wanted on an output.
For an input, it should directly call start_frame or filter_frame on
the corresponding output.
For an input, it should directly call filter_frame on the corresponding
output.
For a filter, if there are queued frames already ready, one of these
frames should be pushed. If not, the filter should request a frame on
@ -255,7 +241,7 @@ Frame scheduling
}
while (!frame_pushed) {
input = input_where_a_frame_is_most_needed();
ret = avfilter_request_frame(input);
ret = ff_request_frame(input);
if (ret == AVERROR_EOF) {
process_eof_on_input();
} else if (ret < 0) {
@ -266,4 +252,14 @@ Frame scheduling
Note that, except for filters that can have queued frames, request_frame
does not push frames: it requests them to its input, and as a reaction,
the start_frame / filter_frame method will be called and do the work.
the filter_frame method will be called and do the work.
Legacy API
==========
Until libavfilter 3.23, the filter_frame method was split:
- for video filters, it was made of start_frame, draw_slice (that could be
called several times on distinct parts of the frame) and end_frame;
- for audio filters, it was called filter_samples.

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