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