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40 lines
1.9 KiB
Text
40 lines
1.9 KiB
Text
OUTDATED, EARLY IDEA
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When two pads are connected, a negotiation phase is going to have to
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happen. Ideally, the caps of the two pads will both be fully-specified,
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and match. That's the ideal case, but may rarely happen in practice.
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It'll work the following way:
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1) gst_pad_connect(pad1,pad2) is called by something
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2) pad1's negotiate() method is called, with pad2 as argument
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3) negotiate() repeatedly calls pad2's set_caps() method
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At some point, the two pads will agree on a set of caps, and proceed by
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returning TRUE from negotiate(), at which point gst_pad_connect()
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finishes. If it returns FALSE, gst_pad_connect() is forced to fail.
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Now, obviously the algorithm used to find matching caps can get
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complicated. But in some cases it'll be simple. Ideally, if there is no
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negotiate() function for pad1, there'll be a function that will go through
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the options and try to make pad1 and pad2 meet in the middle, with no
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specific knowledge of what the caps actually mean.
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Another detail is deciding which pads are pad1 and pad2. In the autoplug
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case, the code will sometimes know which of the pads have the more
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specific caps. In others, you may not. Either you can guess, and
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possibly lose to having the slower of the two pad's negotiate() methods do
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the work, or you might be able to actually guess at which is the most
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specific set of caps:
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For any given typeid in the union of both pads, look at all properties
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For each property, find the smallest range, assign this a 1.0
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For all other instances of this property, assign relative to 1.0
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For each pad1,pad2
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Take the assigned value of every property, and multiply together
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Whichever value is lower between pad1 and pad2 is most likely to be the
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most specific set of caps. The trick is implementing the above
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efficiently, but on the surface there appear to be more than enough
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potential optimizations.
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