This is an alternative function used to open and initialize an
cannam@86: OggVorbis_File structure when using a data source other than a file,
cannam@86: when its necessary to modify default file access behavior, or to
cannam@86: initialize a Vorbis decode from a FILE * pointer under
cannam@86: Windows where ov_open() cannot be used. It
cannam@86: allows the application to specify custom file manipulation routines
cannam@86: and sets up all the related decoding structures.
cannam@86:
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Once ov_open_callbacks() has been called, the same
cannam@86: OggVorbis_File struct should be passed to all the
cannam@86: libvorbisfile functions. Unlike ov_fopen() and ov_open(), ov_open_callbacks() may be used to
cannam@86: instruct vorbisfile to either automatically close or not to close the
cannam@86: file/data access handle in ov_clear().
cannam@86: Automatic closure is disabled by passing NULL as the close callback,
cannam@86: or using one of the predefined callback sets that specify a NULL close
cannam@86: callback. The application is responsible for closing a file when a
cannam@86: call to ov_open_callbacks() is unsuccessful.
cannam@86:
cannam@86: See also Callbacks and Non-stdio I/O for
cannam@86: information on designing and specifying custom callback functions.
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cannam@86: int ov_open_callbacks(void *datasource, OggVorbis_File *vf, char *initial, long ibytes, ov_callbacks callbacks);
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Parameters
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datasource
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Pointer to a data structure allocated by the calling application, containing any state needed by the callbacks provided.
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vf
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A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
cannam@86: functions. Once this has been called, the same OggVorbis_File
cannam@86: struct should be passed to all the libvorbisfile functions.
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initial
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Typically set to NULL. This parameter is useful if some data has already been
cannam@86: read from the stream and the stream is not seekable. It is used in conjunction with ibytes. In this case, initial
cannam@86: should be a pointer to a buffer containing the data read.
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ibytes
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Typically set to 0. This parameter is useful if some data has already been
cannam@86: read from the stream and the stream is not seekable. In this case, ibytes
cannam@86: should contain the length (in bytes) of the buffer. Used together with initial.
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callbacks
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A completed ov_callbacks struct which indicates desired custom file manipulation routines. vorbisfile.h defines several preprovided callback sets; see ov_callbacks for details.
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Return Values
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0 for success
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less than zero for failure:
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OV_EREAD - A read from media returned an error.
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OV_ENOTVORBIS - Bitstream does not contain any Vorbis data.
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OV_EVERSION - Vorbis version mismatch.
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OV_EBADHEADER - Invalid Vorbis bitstream header.
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OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.
cannam@86:
cannam@86: ... provides exactly the same functionality as ov_open() but will always work correctly under
cannam@86: Windows, regardless of linking setup details.
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[b] Threaded decode
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If your decoder is threaded, it is recommended that you NOT call
cannam@86: ov_open_callbacks()
cannam@86: in the main control thread--instead, call ov_open_callbacks() in your decode/playback
cannam@86: thread. This is important because ov_open_callbacks() may be a fairly time-consuming
cannam@86: call, given that the full structure of the file is determined at this point,
cannam@86: which may require reading large parts of the file under certain circumstances
cannam@86: (determining all the logical bitstreams in one physical bitstream, for
cannam@86: example). See Thread Safety for other information on using libvorbisfile with threads.
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[c] Mixed media streams
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cannam@86: As of Vorbisfile release 1.2.0, Vorbisfile is able to access the
cannam@86: Vorbis content in mixed-media Ogg streams, not just Vorbis-only
cannam@86: streams. For example, Vorbisfile may be used to open and access the
cannam@86: audio from an Ogg stream consisting of Theora video and Vorbis audio.
cannam@86: Vorbisfile 1.2.0 decodes the first logical audio stream of each
cannam@86: physical stream section.
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[d] Faster testing for Vorbis files
cannam@86:
ov_test() and ov_test_callbacks() provide less
cannam@86: computationally expensive ways to test a file for Vorbisness, but
cannam@86: require more setup code.