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35 lines
1.7 KiB
Text
35 lines
1.7 KiB
Text
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Windows Media works in an asynchronous manner.
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The WM Decompressor (IWMReader) requires that you provide a class
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deriving from IWMReader (and, optionally, IWMReaderAdvanced) to receive information
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Each delivery of uncompressed media arrives in an OnSample method
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Status messages arrive in an OnStatus method.
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The main difficulty that arrives from this approach is that ALL messages funnel through
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a single function. Audio data and Video data arrive in the same function.
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Even worse, status messages for file opened, clock error, http buffering, and DRM requirements all arrive in the same function!
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In order to handle this properly, a "chain of event handlers" class was developed (WMHandler)
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Any object wishing to receive data or status messages can derive from the WMHandler. All unhandled
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messages are automatically passed to the next handler in the chain. Messages that are handled can be
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passed or not passed based on programming requirements.
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The main object sets up the chain. The >> operator has been convienently defined to faciliate the chaining.
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The left side of the >> line must be the source (WMCallback)
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(e.g. callback >> clock >> drm >> video >> audio >> wait >> this;)
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Handlers may create their own mini-chains (which will get added in-whole) using the WMHandler::Inject() method.
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Threading
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------
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7 basic threads
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1. Main (Windows) thread
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2. Callback/OnStatus thread
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3. Audio Decoder thread
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4. Video Decoder thread
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5. Audio buffering thread (ours)
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6. Video buffering thread (ours)
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7. Buffering-percent status thread (ours)
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There might be additional threads (created in another module) calling in, for functions like getextendedfileinfo
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