1 /*! \page usage_decode Decoding 2 3 The vpx_codec_decode() function is at the core of the decode loop. It 4 processes packets of compressed data passed by the application, producing 5 decoded images. The decoder expects packets to comprise exactly one image 6 frame of data. Packets \ref MUST be passed in decode order. If the 7 application wishes to associate some data with the frame, the 8 <code>user_priv</code> member may be set. The <code>deadline</code> 9 parameter controls the amount of time in microseconds the decoder should 10 spend working on the frame. This is typically used to support adaptive 11 \ref usage_postproc based on the amount of free CPU time. For more 12 information on the <code>deadline</code> parameter, see \ref usage_deadline. 13 14 \ref samples 15 16 17 \section usage_cb Callback Based Decoding 18 There are two methods for the application to access decoded frame data. Some 19 codecs support asynchronous (callback-based) decoding \ref usage_features 20 that allow the application to register a callback to be invoked by the 21 decoder when decoded data becomes available. Decoders are not required to 22 support this feature, however. Like all \ref usage_features, support can be 23 determined by calling vpx_codec_get_caps(). Callbacks are available in both 24 frame-based and slice-based variants. Frame based callbacks conform to the 25 signature of #vpx_codec_put_frame_cb_fn_t and are invoked once the entire 26 frame has been decoded. Slice based callbacks conform to the signature of 27 #vpx_codec_put_slice_cb_fn_t and are invoked after a subsection of the frame 28 is decoded. For example, a slice callback could be issued for each 29 macroblock row. However, the number and size of slices to return is 30 implementation specific. Also, the image data passed in a slice callback is 31 not necessarily in the same memory segment as the data will be when it is 32 assembled into a full frame. For this reason, the application \ref MUST 33 examine the rectangles that describe what data is valid to access and what 34 data has been updated in this call. For all their additional complexity, 35 slice based decoding callbacks provide substantial speed gains to the 36 overall application in some cases, due to improved cache behavior. 37 38 39 \section usage_frame_iter Frame Iterator Based Decoding 40 If the codec does not support callback based decoding, or the application 41 chooses not to make use of that feature, decoded frames are made available 42 through the vpx_codec_get_frame() iterator. The application initializes the 43 iterator storage (of type #vpx_codec_iter_t) to NULL, then calls 44 vpx_codec_get_frame repeatedly until it returns NULL, indicating that all 45 images have been returned. This process may result in zero, one, or many 46 frames that are ready for display, depending on the codec. 47 48 49 \section usage_postproc Postprocessing 50 Postprocessing is a process that is applied after a frame is decoded to 51 enhance the image's appearance by removing artifacts introduced in the 52 compression process. It is not required to properly decode the frame, and 53 is generally done only when there is enough spare CPU time to execute 54 the required filters. Codecs may support a number of different 55 postprocessing filters, and the available filters may differ from platform 56 to platform. Embedded devices often do not have enough CPU to implement 57 postprocessing in software. The filter selection is generally handled 58 automatically by the codec, depending on the amount of time remaining before 59 hitting the user-specified \ref usage_deadline after decoding the frame. 60 61 62 */ 63
