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88 lines
4.8 KiB
Text
88 lines
4.8 KiB
Text
### design proposal for metadata mux and parser ###
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## use cases ##
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1- Create metadata
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[ App send tag events to the pipeline ]
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|| /\
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|| ||
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|| jpegenc send tag messages like (width, height and compression info)
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|| ||
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\/ ||
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+---------+ +---------+ +-------------+ +----------+
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| v4l2src | -> | jpegenc | -> | metadatamux | -> | filesink |
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+---------+ +---------+ +-------------+ +----------+
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* elements like videoscale should also send (width and height tags)
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* should metadatamux get info from caps (width and height) and use if not receive a event with such tags?
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2- View metadata
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+---------+ +---------------+ +---------+ +-------------+
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| filesrc | -> | metadataparse | -> | jpegdec | -> | xvimagesink |
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+---------+ +---------------+ +---------+ +-------------+
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or
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+--> whole chunk send as event to next element
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+---------+ +---------------+ +----------+
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| filesrc | -> | metadataparse | -> | fakesink |
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+---------+ +---------------+ +----------+
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||
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\/
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1- individual tags send as messages (what about not mapped tags??)
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2- whole chunk send as message (probably the application will ignore this)
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* in any case metadataparse strips out metadata chunks (different from current implementation)
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3- Modify (add, change, delete tags)
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+--> whole chunk send as event to next element -- ... --+
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| V
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+---------+ +---------------+ +-------------+ +----------+
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| filesrc | -> | metadataparse | --------------- ... --------------> | metadatamux | -> | filesink |
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+---------+ +---------------+ +-------------+ +----------+
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/\ ||
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|| \/
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|| 1- individual tags send as messages (what about not mapped tags??) ==============\\
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|| 2- whole chunk send as message (probably the application will ignore this) ||
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|| ||
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[ App send tag events to the pipeline ] <=======================================================//
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* metadataparse strips out metadata chunks (different from current implementation)
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* application receives individual tag messages (what about not mapped ones?)
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* the application only send events back to the pipeline for the tags the application wants to modify or keep.
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The tags not sent will not be included in metadata chunks
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* the metadatamux modify the whole chunk event received before to just keep the individual tags sent by application
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* the metadatamux could have a property to say if it should remove or keep tags not sent by application.
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Obs: By looking at the proposed design (1- view and 2- modify) seems that the metadataparse and metadatamux should not know about mapped tags.
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Only the application map the tags to/from metadata specific format. This is because, if you notice, only tags sent by application will be keep
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on new file.
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4- Convert (for example from jpeg to png)
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+--> whole chunk send as event to next element -- ... --+
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| V
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+---------+ +---------------+ +-------------+ +----------+
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| filesrc | -> | metadataparse | -> | jpegdec | -> ... -> | pngenc | -> | metadatamux | -> | filesink |
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+---------+ +---------------+ +-------------+ +----------+
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/\ ||
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|| \/
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|| 1- individual tags send as messages (what about not mapped tags??) ==============\\
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|| 2- whole chunk send as message (probably the application will ignore this) ||
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|| ||
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[ App send tag events to the pipeline ] <=======================================================//
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* in this case the application set the metadatamux property to always keep the tags by default (application don't not need to send tag events)
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* metadatamux needs additional smartness to check what tags still does make sense (some from original jpeg may not make sense anymore)
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* if the image is resized, the videoscale should send messages to the application with new width (in the same way pngenc should also) and the
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application could send width and height tag events to the pipeline
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* should metadatamux get info from caps (width and height) and use if not receive a event with such tags?
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