1/*!\page usage Usage
2
3    The aom multi-format codec SDK provides a unified interface amongst its
4    supported codecs. This abstraction allows applications using this SDK to
5    easily support multiple video formats with minimal code duplication or
6    "special casing." This section describes the interface common to all codecs.
7    For codec-specific details, see the \ref codecs page.
8
9    The following sections are common to all codecs:
10    - \ref usage_types
11    - \ref usage_features
12    - \ref usage_init
13    - \ref usage_errors
14
15    For more information on decoder and encoder specific usage, see the
16    following pages:
17    \if decoder
18    \li \subpage usage_decode
19    \endif
20    \if encoder
21    \li \subpage usage_encode
22    \endif
23
24    \section usage_types Important Data Types
25    There are two important data structures to consider in this interface.
26
27    \subsection usage_ctxs Contexts
28    A context is a storage area allocated by the calling application that the
29    codec may write into to store details about a single instance of that codec.
30    Most of the context is implementation specific, and thus opaque to the
31    application. The context structure as seen by the application is of fixed
32    size, and thus can be allocated with automatic storage or dynamically
33    on the heap.
34
35    Most operations require an initialized codec context. Codec context
36    instances are codec specific. That is, the codec to be used for the encoded
37    video must be known at initialization time. See #aom_codec_ctx_t for further
38    information.
39
40    \subsection usage_ifaces Interfaces
41    A codec interface is an opaque structure that controls how function calls
42    into the generic interface are dispatched to their codec-specific
43    implementations. Applications \ref MUSTNOT attempt to examine or override
44    this storage, as it contains internal implementation details likely to
45    change from release to release.
46
47    Each supported codec will expose an interface structure to the application
48    as an <code>extern</code> reference to a structure of the incomplete type
49    #aom_codec_iface_t.
50
51    \section usage_features Features
52    Several "features" are defined that are optionally implemented by codec
53    algorithms. Indeed, the same algorithm may support different features on
54    different platforms. The purpose of defining these features is that when
55    they are implemented, they conform to a common interface. The features, or
56    capabilities, of an algorithm can be queried from it's interface by using
57    the aom_codec_get_caps() method. Attempts to invoke features not supported
58    by an algorithm will generally result in #AOM_CODEC_INCAPABLE.
59
60    \if decoder
61    Currently defined decoder features include:
62    \endif
63
64    \section usage_init Initialization
65    To initialize a codec instance, the address of the codec context
66    and interface structures are passed to an initialization function. Depending
67    on the \ref usage_features that the codec supports, the codec could be
68    initialized in different modes.
69
70    To prevent cases of confusion where the ABI of the library changes,
71    the ABI is versioned. The ABI version number must be passed at
72    initialization time to ensure the application is using a header file that
73    matches the library. The current ABI version number is stored in the
74    preprocessor macros #AOM_CODEC_ABI_VERSION, #AOM_ENCODER_ABI_VERSION, and
75    #AOM_DECODER_ABI_VERSION. For convenience, each initialization function has
76    a wrapper macro that inserts the correct version number. These macros are
77    named like the initialization methods, but without the _ver suffix.
78
79
80    The available initialization methods are:
81    \if encoder
82    \li #aom_codec_enc_init (calls aom_codec_enc_init_ver())
83    \endif
84    \if decoder
85    \li #aom_codec_dec_init (calls aom_codec_dec_init_ver())
86    \endif
87
88
89    \section usage_errors Error Handling
90    Almost all codec functions return an error status of type #aom_codec_err_t.
91    The semantics of how each error condition should be processed is clearly
92    defined in the definitions of each enumerated value. Error values can be
93    converted into ASCII strings with the aom_codec_error() and
94    aom_codec_err_to_string() methods. The difference between these two methods is
95    that aom_codec_error() returns the error state from an initialized context,
96    whereas aom_codec_err_to_string() can be used in cases where an error occurs
97    outside any context. The enumerated value returned from the last call can be
98    retrieved from the <code>err</code> member of the decoder context as well.
99    Finally, more detailed error information may be able to be obtained by using
100    the aom_codec_error_detail() method. Not all errors produce detailed error
101    information.
102
103    In addition to error information, the codec library's build configuration
104    is available at runtime on some platforms. This information can be returned
105    by calling aom_codec_build_config(), and is formatted as a base64 coded string
106    (comprised of characters in the set [a-z_a-Z0-9+/]). This information is not
107    useful to an application at runtime, but may be of use to aom for support.
108
109*/
110