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39 lines
2.3 KiB
Text
39 lines
2.3 KiB
Text
You might start by creating a source element and put it into a pipeline.
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At this point both element's state would be GST_STATE_NEW, since they
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don't have enough state to actually run yet. At this point you can set
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the filename of the source, and possibly bytesperread and other things.
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Then you'd want to discover the data type of the file you're sourcing.
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This will typically be handled by the pipeline itself by calling
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gst_pipeline_autoplug(), or gst_pipeline_find_pad_type(), or somesuch. The
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pipeline would first set its state to GST_STATE_DISCOVERY. A gstfindtype
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sink would be added to the pipeline and connected to the source. Its
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HAVE_TYPE signal would be connected to a private pipeline function.
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The pipeline would then set the the src state to GST_STATE_DISCOVERY, and
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call the src's push() function until a the type is set by the function
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connected to the gstfindtype element's signal. At this point the pipeline
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would disconnect the gstfindtype element from the src, set the type of the
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pad to the type returned by the gstfindtype element. At disconnection of
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the find element, the src's state automatically reverts to NEW.
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(The trick with the sources when they do DISCOVERY is that synchronous
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sources can't go back and read data again. So perhaps I should set up a
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wrapper function for the push() function that uses either a sync or
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async function as provided by the src instance to provide DISCOVERY and
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normal operations. It would use a [GstBufferCache] to read ahead into
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memory if necessary, creating baby buffers as necessary to answer the
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needs of each DISCOVERY sequence.)
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If you called find_pad_type(), it would return right about now, with the
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ID of the type it found. At the same time, if you have connected a signal
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to the pad's SET_TYPE signal, it would fire right as the type is set by
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the find_pad_type() function. This would allow your application to do its
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own selection of filters to connect to the pad.
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If you called autoplug(), the pipeline would make a selection of element
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to connect. The element would be created (state=NEW), added to the
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pipeline, and the appropriate sink pad connected to the src in question.
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(Note that multi-sink elements won't be supported unless there's a really
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good and obvious way to do so) The whole process would repeat until the
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recently added element no longer has a src pad.
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