GstFlowCombiner: GStreamer Library Reference Manual

## GstFlowCombiner GstFlowCombiner — Utility to combine multiple flow returns into one |

## Functions

GstFlowCombiner * | gst_flow_combiner_new ()
void | gst_flow_combiner_free ()
GstFlowCombiner * | gst_flow_combiner_ref ()
void | gst_flow_combiner_unref ()
GstFlowReturn | gst_flow_combiner_update_flow ()
void | gst_flow_combiner_add_pad ()
void | gst_flow_combiner_remove_pad ()
void | gst_flow_combiner_clear ()
void | gst_flow_combiner_reset ()
GstFlowReturn | gst_flow_combiner_update_pad_flow ()

## Types and Values

| GstFlowCombiner

## Includes

    #include <gst/base/base.h>

## Description

Utility struct to help handling GstFlowReturn combination. Useful for GstElements that have multiple source pads and need to combine the different GstFlowReturn for those pads.

GstFlowCombiner works by using the last GstFlowReturn for all GstPad it has in its list and computes the combined return value and provides it to the caller.

To add a new pad to the GstFlowCombiner use `gst_flow_combiner_add_pad()`. The new GstPad is stored with a default value of `GST_FLOW_OK`.

In case you want a GstPad to be removed, use `gst_flow_combiner_remove_pad()`.

Please be aware that this struct isn't thread safe as its designed to be used by demuxers, those usually will have a single thread operating it.

These functions will take refs on the passed GstPads.

Aside from reducing the user's code size, the main advantage of using this helper struct is to follow the standard rules for GstFlowReturn combination. These rules are:

- `GST_FLOW_EOS`: only if all returns are EOS too

- `GST_FLOW_NOT_LINKED`: only if all returns are NOT_LINKED too

- `GST_FLOW_ERROR` or below: if at least one returns an error return

- `GST_FLOW_NOT_NEGOTIATED`: if at least one returns a not-negotiated return

- `GST_FLOW_FLUSHING`: if at least one returns flushing

- `GST_FLOW_OK`: otherwise

`GST_FLOW_ERROR` or below, GST_FLOW_NOT_NEGOTIATED and GST_FLOW_FLUSHING are returned immediately from the `gst_flow_combiner_update_flow()` function.

## Functions

### gst_flow_combiner_new ()

    GstFlowCombiner *
    gst_flow_combiner_new (void);

Creates a new GstFlowCombiner, use `gst_flow_combiner_free()` to free it.

#### Returns

A new GstFlowCombiner

Since: 1.4

### gst_flow_combiner_free ()

    void
    gst_flow_combiner_free (GstFlowCombiner *combiner);

Frees a GstFlowCombiner struct and all its internal data.

#### Parameters

combiner | the GstFlowCombiner to free |

Since: 1.4

### gst_flow_combiner_ref ()

    GstFlowCombiner *
    gst_flow_combiner_ref (GstFlowCombiner *combiner);

Increments the reference count on the GstFlowCombiner.

#### Parameters

combiner | the GstFlowCombiner to add a reference to. |

#### Returns

the GstFlowCombiner.

Since: 1.12.1

### gst_flow_combiner_unref ()

    void
    gst_flow_combiner_unref (GstFlowCombiner *combiner);

Decrements the reference count on the GstFlowCombiner.

#### Parameters

combiner | the GstFlowCombiner to unreference. |

Since: 1.12.1

### gst_flow_combiner_update_flow ()

    GstFlowReturn
    gst_flow_combiner_update_flow (GstFlowCombiner *combiner,
                                   GstFlowReturn fret);

Computes the combined flow return for the pads in it.

The GstFlowReturn parameter should be the last flow return update for a pad in this GstFlowCombiner. It will use this value to be able to shortcut some combinations and avoid looking over all pads again. e.g. The last combined return is the same as the latest obtained GstFlowReturn.

#### Parameters

combiner | the GstFlowCombiner |
fret | the latest GstFlowReturn received for a pad in this GstFlowCombiner |

#### Returns

The combined GstFlowReturn

Since: 1.4

### gst_flow_combiner_add_pad ()

    void
    gst_flow_combiner_add_pad (GstFlowCombiner *combiner,
                               GstPad *pad);

Adds a new GstPad to the GstFlowCombiner.

#### Parameters

combiner | the GstFlowCombiner |
pad | the GstPad that is being added. | [transfer none]

Since: 1.4

### gst_flow_combiner_remove_pad ()

    void
    gst_flow_combiner_remove_pad (GstFlowCombiner *combiner,
                                  GstPad *pad);

Removes a GstPad from the GstFlowCombiner.

#### Parameters

combiner | the GstFlowCombiner |
pad | the GstPad to remove. | [transfer none]

Since: 1.4

### gst_flow_combiner_clear ()

    void
    gst_flow_combiner_clear (GstFlowCombiner *combiner);

Removes all pads from a GstFlowCombiner and resets it to its initial state.

#### Parameters

combiner | the GstFlowCombiner to clear |

Since: 1.6

### gst_flow_combiner_reset ()

    void
    gst_flow_combiner_reset (GstFlowCombiner *combiner);

Reset flow combiner and all pads to their initial state without removing pads.

#### Parameters

combiner | the GstFlowCombiner to clear |

Since: 1.6

### gst_flow_combiner_update_pad_flow ()

    GstFlowReturn
    gst_flow_combiner_update_pad_flow (GstFlowCombiner *combiner,
                                       GstPad *pad,
                                       GstFlowReturn fret);

Sets the provided pad's last flow return to provided value and computes the combined flow return for the pads in it.

The GstFlowReturn parameter should be the last flow return update for a pad in this GstFlowCombiner. It will use this value to be able to shortcut some combinations and avoid looking over all pads again. e.g. The last combined return is the same as the latest obtained GstFlowReturn.

#### Parameters

combiner | the GstFlowCombiner |
pad | the GstPad whose GstFlowReturn to update |
fret | the latest GstFlowReturn received for a pad in this GstFlowCombiner |

#### Returns

The combined GstFlowReturn

Since: 1.6

## Types and Values

### GstFlowCombiner

    typedef struct _GstFlowCombiner GstFlowCombiner;

Opaque helper structure to aggregate flow returns.

Since: 1.4