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camerabin2: Adding camera source documentation file

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Adds a small text file with a brief description of
what is expected from a camerabin2 source element
This commit is contained in:
Thiago Santos 2011-04-25 16:04:26 -03:00
parent c86d662b23
commit d8484f8279
1 changed files with 81 additions and 0 deletions
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gst/camerabin2/camerabin2-src.txt Normal file
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=== Camerabin2 Source Requirements (draft) ===
This small document contains a collection of notes on different requirements
of a camerabin2 source element.
-- General --
It is recommended that camerabin2 source elements inherit from basecamerasrc
from gst-plugins-bad.
-- Pads --
Camerabin2 sources must have 3 static pads named 'vfsrc', 'imgsrc' and
'vidsrc'.
From an external point of view, all 3 pads work independently and camerabin2
makes no assumptions about relations about them (caps they can produce, or if
the same buffer is pushed to 2 different pads).
'vfsrc' is the pad where the viewfinder buffers should be pushed, it will
be feeding a video sink. This is the same scenario as a 'regular' source
feeding a video sink. Buffers should be continuously pushed on this pad.
'imgsrc' is the pad where image capture buffers are pushed. Timestamps aren't
really important here as the images are going to be encoded and saved
separately from each other. For each capture in image mode, one buffer should
be pushed on this pad.
'vidsrc' is the pad where video capture buffers are pushed. Once capture is
started, buffers should start being pushed on this pad until the capture is
stopped.
-> TODO - define how segments/timestamps should work here
-> TODO - How to make audio and video sync properly
-- Capture --
The sources should have a 'mode' property that informs the source of the
current capturing mode. The available options are image or video.
There are 2 signals that should be implemented, start-capture and
stop-capture, they take no arguments.
On image mode, start-capture tells the source to push an image capture
buffer on its imgsrc pad. For video mode, start-capture tells the source
to start pushing buffers on the vidsrc pad, it should only stop
pushing when a stop-capture signal is received. In either case, it is
recommended that the viewfinder pad keeps pushing buffers so the user
has a smooth experience.
Note that basecamerasrc already has the mode property and start/stop-capture
signals. It has functions that should be overriden by its child classes to
implement the handling of these actions.
-- Previews --
Camerabin2 sources must have a post-previews boolean property that the user
can select if we wants or not preview images.
Previews are posted on the bus as custom 'preview-image' messages. This message
must have a 'buffer' field that contains a GstBuffer, the preview.
Additionally, there should be a preview-caps property that is used to inform the
camera source what is the expected format of the preview image.
A preview image should be posted for each capture.
-- Negotiation --
Capture caps selection on camerabin2 works just like gstreamer's default
caps negotiation. Camerabin2 puts capsfilters downstream from each of the
camera source pads. The camera source can simply get_caps on the peer of
each of its pads to know what are the allowed caps for that pad.
-- Renegotiation --
Easy renegotiation isn't supported on gstreamer yet (there is some ongoing work
currently). Camerabin2 will use a custom 'renegotiate' event, no fields to
indicate that a certain pad should renegotiate its caps.
Upon receiving this event, a pad should get_caps on its peer and do the caps
negotiation again. It is likely that a new format was requested.