Annotation of /trunk/xvidcore/doc/xvid-decoding.txt

1 :	Isibaar	3	/*************************************************************
2 :			* Short explanation for the XviD data strutures and routines
3 :			*
4 :			* decoding part
5 :			*
6 :			* if you have further questions, visit http://www.xvid.org
7 :			*
8 :			**************************************************************/
9 :
10 :			/* these are are structures/routines from xvid.h needed for decoding */
11 :
12 :			--------------------------------------------------------------------------
13 :
14 :			#define API_VERSION ((1 << 16) \| (0))
15 :
16 :			This is the revision of the xvid.h file that you have in front of you.
17 :			Check it against the
18 :			library's version.
19 :
20 :			--------------------------------------------------------------------------
21 :
22 :			typedef struct
23 :			{
24 :			int cpu_flags; [in/out]
25 :			int api_version; [out]
26 :			int core_build; [out]
27 :			} XVID_INIT_PARAM;
28 :
29 :			This is filled by xvid_init with the correct CPU flags for initialization
30 :			(auto-detect), unless you pass flag to it (cpu_flags!=0). Do not use that
31 :			unless you really know what you are doing.
32 :			api_version can (should) be checked against API_VERSION, to see if you
33 :			have the right core library.
34 :
35 :			Used in: xvid_init(NULL, 0, &xinit, NULL);
36 :
37 :			--------------------------------------------------------------------------
38 :
39 :			typedef struct
40 :			{
41 :			int width; [in] (should be a multiple of 16, max is )
42 :			int height; [in] (should be a multiple of 16, max is )
43 :			void *handle; [out]
44 :			} XVID_DEC_PARAM;
45 :
46 :			When creating decoder, you have to provide it with height and width of the
47 :			image to decode (this is _not_ in the bytestream itself!).
48 :			In handle a unique handle is given back, that has to be used to identify
49 :			this instance of decoding.
50 :
51 :			Used in: xerr = xvid_decore(NULL, XVID_DEC_CREATE, &xparam, NULL);
52 :
53 :			--------------------------------------------------------------------------
54 :
55 :			typedef struct
56 :			{
57 :			void * bitstream; [in]
58 :			int length; [in]
59 :
60 :			void * image; [in]
61 :			int stride; [in]
62 :			int colorspace; [in]
63 :			} XVID_DEC_FRAME;
64 :
65 :			This is the main structure for decoding itself. You provide the
66 :			MPEG4-bitstream and it's length,
67 :			image is the position where the decoded picture should be stored.
68 :			stride is the difference between the memory address of the first pixel of
69 :			a row in the image and the first pixel of the next row. If the image is
70 :			going to be one big block, then stride=width, but by making it larger you
71 :			can create an "edged" picture.
72 :			By colorspace the output format for the image is given, XVID_CSP_RGB24 or
73 :			XVID_CSP_YV12 might be might common.
74 :
75 :			A special case is XVID_CSP_USER. If you use this, then *image will not
76 :			filled with the image but with a structure that contains pointers to the
77 :			decoder's internal representation of it. That's faster, because no memcopy
78 :			is involved, but don't use it, if you don't know what you're doing.
79 :
80 :			Used in: xerr = xvid_decore(dechandle, XVID_DEC_DECODE, &xframe, NULL);
81 :
82 :			--------------------------------------------------------------------------
83 :
84 :			int xvid_decore(void * handle, [in/out]
85 :			int opt, [in]
86 :			void * param1, [in]
87 :			void * param2); [in]
88 :
89 :
90 :			XviD uses a single-function API, so everything you want to do is done by
91 :			this routine. The opt parameter chooses the behaviour of the routine:
92 :
93 :			XVID_DEC_CREATE: create a new decoder, XVID_DEC_PARAM in param1,
94 :			a handle to the new decoder is returned in handle
95 :
96 :			XVID_DEC_DECODE: decode one frame, XVID_DEC_FRAME-structure in param1
97 :
98 :			XVID_DEC_DESTROY: shut down this decoder, do not use handle afterwards

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