## GstTypeFindHelper

GstTypeFindHelper — Utility functions for typefinding

## Synopsis

    #include <gst/base/gsttypefindhelper.h>

    GstCaps *           gst_type_find_helper                (GstPad *src,
                                                             guint64 size);
    GstCaps *           gst_type_find_helper_for_buffer     (GstObject *obj,
                                                             GstBuffer *buf,
                                                             GstTypeFindProbability *prob);
    GstCaps *           gst_type_find_helper_for_extension  (GstObject *obj,
                                                             const gchar *extension);
    GstCaps *           gst_type_find_helper_for_data       (GstObject *obj,
                                                             const guint8 *data,
                                                             gsize size,
                                                             GstTypeFindProbability *prob);
    GstFlowReturn       (*GstTypeFindHelperGetRangeFunction)
                                                            (GstObject *obj,
                                                             GstObject *parent,
                                                             guint64 offset,
                                                             guint length,
                                                             GstBuffer **buffer);
    GstCaps *           gst_type_find_helper_get_range      (GstObject *obj,
                                                             GstObject *parent,
                                                             GstTypeFindHelperGetRangeFunction func,
                                                             guint64 size,
                                                             const gchar *extension,
                                                             GstTypeFindProbability *prob);

## Description

Utility functions for elements doing typefinding: `gst_type_find_helper()` does typefinding in pull mode, while `gst_type_find_helper_for_buffer()` is useful for elements needing to do typefinding in push mode from a chain function.

## Details

### gst_type_find_helper ()

    GstCaps *           gst_type_find_helper                (GstPad *src,
                                                             guint64 size);

Tries to find what type of data is flowing from the given source GstPad.

Free-function: gst_caps_unref

`src` : | A source GstPad
`size` : | The length in bytes
Returns : | the GstCaps corresponding to the data stream. Returns NULL if no GstCaps matches the data stream. [transfer full]

### gst_type_find_helper_for_buffer ()

    GstCaps *           gst_type_find_helper_for_buffer     (GstObject *obj,
                                                             GstBuffer *buf,
                                                             GstTypeFindProbability *prob);

Tries to find what type of data is contained in the given GstBuffer, the assumption being that the buffer represents the beginning of the stream or file.

All available typefinders will be called on the data in order of rank. If a typefinding function returns a probability of GST_TYPE_FIND_MAXIMUM, typefinding is stopped immediately and the found caps will be returned right away. Otherwise, all available typefind functions will the tried, and the caps with the highest probability will be returned, or NULL if the content of the buffer could not be identified.

Free-function: gst_caps_unref

`obj` : | object doing the typefinding, or NULL (used for logging). [allow-none]
`buf` : | a GstBuffer with data to typefind. [in][transfer none]
`prob` : | location to store the probability of the found caps, or NULL. [out][allow-none]
Returns : | the GstCaps corresponding to the data, or NULL if no type could be found. The caller should free the caps returned with `gst_caps_unref()`. [transfer full]

### gst_type_find_helper_for_extension ()

    GstCaps *           gst_type_find_helper_for_extension  (GstObject *obj,
                                                             const gchar *extension);

Tries to find the best GstCaps associated with `extension`.

All available typefinders will be checked against the extension in order of rank. The caps of the first typefinder that can handle `extension` will be returned.

Free-function: gst_caps_unref

`obj` : | object doing the typefinding, or NULL (used for logging). [allow-none]
`extension` : | an extension
Returns : | the GstCaps corresponding to `extension`, or NULL if no type could be found. The caller should free the caps returned with `gst_caps_unref()`. [transfer full]

### gst_type_find_helper_for_data ()

    GstCaps *           gst_type_find_helper_for_data       (GstObject *obj,
                                                             const guint8 *data,
                                                             gsize size,
                                                             GstTypeFindProbability *prob);

Tries to find what type of data is contained in the given `data`, the assumption being that the data represents the beginning of the stream or file.

All available typefinders will be called on the data in order of rank. If a typefinding function returns a probability of GST_TYPE_FIND_MAXIMUM, typefinding is stopped immediately and the found caps will be returned right away. Otherwise, all available typefind functions will the tried, and the caps with the highest probability will be returned, or NULL if the content of `data` could not be identified.

Free-function: gst_caps_unref

`obj` : | object doing the typefinding, or NULL (used for logging). [allow-none]
`data` : | a pointer with data to typefind. [in][transfer none]
`size` : | the size of `data`. [in][transfer none]
`prob` : | location to store the probability of the found caps, or NULL. [out][allow-none]
Returns : | the GstCaps corresponding to the data, or NULL if no type could be found. The caller should free the caps returned with `gst_caps_unref()`. [transfer full]

### GstTypeFindHelperGetRangeFunction ()

    GstFlowReturn       (*GstTypeFindHelperGetRangeFunction)
                                                            (GstObject *obj,
                                                             GstObject *parent,
                                                             guint64 offset,
                                                             guint length,
                                                             GstBuffer **buffer);

This function will be called by `gst_type_find_helper_get_range()` when typefinding functions request to peek at the data of a stream at certain offsets. If this function returns GST_FLOW_OK, the result buffer will be stored in `buffer`. The contents of `buffer` is invalid for any other return value.

This function is supposed to behave exactly like a GstPadGetRangeFunction.

`obj` : | a GstObject that will handle the getrange request
`parent` : | the parent of `obj` or NULL. [allow-none]
`offset` : | the offset of the range
`length` : | the length of the range
`buffer` : | a memory location to hold the result buffer
Returns : | GST_FLOW_OK for success

### gst_type_find_helper_get_range ()

    GstCaps *           gst_type_find_helper_get_range      (GstObject *obj,
                                                             GstObject *parent,
                                                             GstTypeFindHelperGetRangeFunction func,
                                                             guint64 size,
                                                             const gchar *extension,
                                                             GstTypeFindProbability *prob);

Utility function to do pull-based typefinding. Unlike `gst_type_find_helper()` however, this function will use the specified function `func` to obtain the data needed by the typefind functions, rather than operating on a given source pad. This is useful mostly for elements like tag demuxers which strip off data at the beginning and/or end of a file and want to typefind the stripped data stream before adding their own source pad (the specified callback can then call the upstream peer pad with offsets adjusted for the tag size, for example).

When `extension` is not NULL, this function will first try the typefind functions for the given extension, which might speed up the typefinding in many cases.

Free-function: gst_caps_unref

`obj` : | A GstObject that will be passed as first argument to `func`
`parent` : | the parent of `obj` or NULL. [allow-none]
`func` : | A generic GstTypeFindHelperGetRangeFunction that will be used to access data at random offsets when doing the typefinding. [scope call]
`size` : | The length in bytes
`extension` : | extension of the media
`prob` : | location to store the probability of the found caps, or NULL. [out][allow-none]
Returns : | the GstCaps corresponding to the data stream. Returns NULL if no GstCaps matches the data stream. [transfer full]