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- /*! \page usage_decode Decoding
- The vpx_codec_decode() function is at the core of the decode loop. It
- processes packets of compressed data passed by the application, producing
- decoded images. The decoder expects packets to comprise exactly one image
- frame of data. Packets \ref MUST be passed in decode order. If the
- application wishes to associate some data with the frame, the
- <code>user_priv</code> member may be set. The <code>deadline</code>
- parameter controls the amount of time in microseconds the decoder should
- spend working on the frame. This is typically used to support adaptive
- \ref usage_postproc based on the amount of free CPU time. For more
- information on the <code>deadline</code> parameter, see \ref usage_deadline.
- \if samples
- \ref samples
- \endif
- \section usage_cb Callback Based Decoding
- There are two methods for the application to access decoded frame data. Some
- codecs support asynchronous (callback-based) decoding \ref usage_features
- that allow the application to register a callback to be invoked by the
- decoder when decoded data becomes available. Decoders are not required to
- support this feature, however. Like all \ref usage_features, support can be
- determined by calling vpx_codec_get_caps(). Callbacks are available in both
- frame-based and slice-based variants. Frame based callbacks conform to the
- signature of #vpx_codec_put_frame_cb_fn_t and are invoked once the entire
- frame has been decoded. Slice based callbacks conform to the signature of
- #vpx_codec_put_slice_cb_fn_t and are invoked after a subsection of the frame
- is decoded. For example, a slice callback could be issued for each
- macroblock row. However, the number and size of slices to return is
- implementation specific. Also, the image data passed in a slice callback is
- not necessarily in the same memory segment as the data will be when it is
- assembled into a full frame. For this reason, the application \ref MUST
- examine the rectangles that describe what data is valid to access and what
- data has been updated in this call. For all their additional complexity,
- slice based decoding callbacks provide substantial speed gains to the
- overall application in some cases, due to improved cache behavior.
- \section usage_frame_iter Frame Iterator Based Decoding
- If the codec does not support callback based decoding, or the application
- chooses not to make use of that feature, decoded frames are made available
- through the vpx_codec_get_frame() iterator. The application initializes the
- iterator storage (of type #vpx_codec_iter_t) to NULL, then calls
- vpx_codec_get_frame repeatedly until it returns NULL, indicating that all
- images have been returned. This process may result in zero, one, or many
- frames that are ready for display, depending on the codec.
- \section usage_postproc Postprocessing
- Postprocessing is a process that is applied after a frame is decoded to
- enhance the image's appearance by removing artifacts introduced in the
- compression process. It is not required to properly decode the frame, and
- is generally done only when there is enough spare CPU time to execute
- the required filters. Codecs may support a number of different
- postprocessing filters, and the available filters may differ from platform
- to platform. Embedded devices often do not have enough CPU to implement
- postprocessing in software. The filter selection is generally handled
- automatically by the codec, depending on the amount of time remaining before
- hitting the user-specified \ref usage_deadline after decoding the frame.
- */
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