Vorbisfile documentation | vorbisfile version 1.2.0 - 20070723

# ov_callbacks

declared in "vorbis/codec.h"

The ov_callbacks structure contains file manipulation function prototypes necessary for opening, closing, seeking, and location.

The ov_callbacks structure does not need to be user-defined if you are working with stdio-based file manipulation; the ov_fopen() and ov_open() calls internally provide default callbacks for stdio. ov_callbacks are defined and passed to ov_open_callbacks() when implementing non-stdio based stream manipulation (such as playback from a memory buffer) or when ov_open()-style initialization from a `FILE *` is required under Windows [a].

    typedef struct {
      size_t (*read_func)  (void *ptr, size_t size, size_t nmemb, void *datasource);
      int    (*seek_func)  (void *datasource, ogg_int64_t offset, int whence);
      int    (*close_func) (void *datasource);
      long   (*tell_func)  (void *datasource);
    } ov_callbacks;

### Relevant Struct Members

read_func
  Pointer to custom data reading function.
seek_func
  Pointer to custom data seeking function. If the data source is not seekable (or the application wants the data source to be treated as unseekable at all times), the provided seek callback should always return -1 (failure) or the `seek_func` and `tell_func` fields should be set to NULL.
close_func
  Pointer to custom data source closure function. Set to NULL if libvorbisfile should not attempt to automatically close the file/data handle.
tell_func
  Pointer to custom data location function. If the data source is not seekable (or the application wants the data source to be treated as unseekable at all times), the provided tell callback should always return -1 (failure) or the `seek_func` and `tell_func` fields should be set to NULL.

### Predefined callbacks

The header vorbis/vorbisfile.h provides several predefined static ov_callbacks structures that may be passed to ov_open_callbacks():

`OV_CALLBACKS_DEFAULT`
  These callbacks provide the same behavior as used internally by ov_fopen() and ov_open().
`OV_CALLBACKS_NOCLOSE`
  The same as `OV_CALLBACKS_DEFAULT`, but with the `close_func` field set to NULL. The most typical use would be to use ov_open_callbacks() to provide the same behavior as ov_open(), but not close the file/data handle in ov_clear().
`OV_CALLBACKS_STREAMONLY`
  A set of callbacks that set `seek_func` and `tell_func` to NULL, thus forcing strict streaming-only behavior regardless of whether or not the input is actually seekable.
`OV_CALLBACKS_STREAMONLY_NOCLOSE`
  The same as `OV_CALLBACKS_STREAMONLY`, but with `close_func` also set to null, preventing libvorbisfile from attempting to close the file/data handle in ov_clear().

### Examples and usage

See the callbacks and non-stdio I/O document for more detailed information on required behavior of the various callback functions.

copyright © 2007 Xiph.org | Ogg Vorbis
Vorbisfile documentation | vorbisfile version 1.2.0 - 20070723