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Diffstat (limited to 'media/libvpx/libvpx/usage_dx.dox')
| -rw-r--r-- | media/libvpx/libvpx/usage_dx.dox | 64 |
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diff --git a/media/libvpx/libvpx/usage_dx.dox b/media/libvpx/libvpx/usage_dx.dox new file mode 100644 index 0000000000..85063f705b --- /dev/null +++ b/media/libvpx/libvpx/usage_dx.dox @@ -0,0 +1,64 @@ +/*! \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. + + +*/ |