## GstCollectPads

GstCollectPads — manages a set of pads that operate in collect mode

## Synopsis

    #include <gst/base/gstcollectpads.h>

                        GstCollectData;
                        GstCollectPads;
    GstFlowReturn       (*GstCollectPadsFunction)           (GstCollectPads *pads,
                                                             gpointer user_data);
    GstBuffer *         (*GstCollectPadsClipFunction)       (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             GstBuffer *buffer,
                                                             gpointer user_data);
    void                (*GstCollectDataDestroyNotify)      (GstCollectData *data);
    GstCollectPads*     gst_collect_pads_new                (void);
    void                gst_collect_pads_set_function       (GstCollectPads *pads,
                                                             GstCollectPadsFunction func,
                                                             gpointer user_data);
    void                gst_collect_pads_set_clip_function  (GstCollectPads *pads,
                                                             GstCollectPadsClipFunction clipfunc,
                                                             gpointer user_data);
    GstCollectData*     gst_collect_pads_add_pad            (GstCollectPads *pads,
                                                             GstPad *pad,
                                                             guint size);
    GstCollectData*     gst_collect_pads_add_pad_full       (GstCollectPads *pads,
                                                             GstPad *pad,
                                                             guint size,
                                                             GstCollectDataDestroyNotify destroy_notify);
    gboolean            gst_collect_pads_remove_pad         (GstCollectPads *pads,
                                                             GstPad *pad);
    gboolean            gst_collect_pads_is_active          (GstCollectPads *pads,
                                                             GstPad *pad);
    GstFlowReturn       gst_collect_pads_collect            (GstCollectPads *pads);
    GstFlowReturn       gst_collect_pads_collect_range      (GstCollectPads *pads,
                                                             guint64 offset,
                                                             guint length);
    void                gst_collect_pads_start              (GstCollectPads *pads);
    void                gst_collect_pads_stop               (GstCollectPads *pads);
    void                gst_collect_pads_set_flushing       (GstCollectPads *pads,
                                                             gboolean flushing);
    GstBuffer*          gst_collect_pads_peek               (GstCollectPads *pads,
                                                             GstCollectData *data);
    GstBuffer*          gst_collect_pads_pop                (GstCollectPads *pads,
                                                             GstCollectData *data);
    guint               gst_collect_pads_available          (GstCollectPads *pads);
    guint               gst_collect_pads_read               (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint8 **bytes,
                                                             guint size);
    GstBuffer *         gst_collect_pads_read_buffer        (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint size);
    GstBuffer *         gst_collect_pads_take_buffer        (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint size);
    guint               gst_collect_pads_flush              (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint size);

## Object Hierarchy

      GObject
       +----GstObject
             +----GstCollectPads

## Description

Manages a set of pads that operate in collect mode. This means that control is given to the manager of this object when all pads have data.

- Collectpads are created with `gst_collect_pads_new()`. A callback should then be installed with `gst_collect_pads_set_function()`.

- Pads are added to the collection with `gst_collect_pads_add_pad()`/ `gst_collect_pads_remove_pad()`. The pad has to be a sinkpad. The chain and event functions of the pad are overridden. The element_private of the pad is used to store private information for the collectpads.

- For each pad, data is queued in the _chain function or by performing a pull_range.

- When data is queued on all pads, the callback function is called.

- Data can be dequeued from the pad with the `gst_collect_pads_pop()` method. One can peek at the data with the `gst_collect_pads_peek()` function. These functions will return NULL if the pad received an EOS event. When all pads return NULL from a `gst_collect_pads_peek()`, the element can emit an EOS event itself.

- Data can also be dequeued in byte units using the `gst_collect_pads_available()`, `gst_collect_pads_read()` and `gst_collect_pads_flush()` calls.

- Elements should call `gst_collect_pads_start()` and `gst_collect_pads_stop()` in their state change functions to start and stop the processing of the collecpads. The `gst_collect_pads_stop()` call should be called before calling the parent element state change function in the PAUSED_TO_READY state change to ensure no pad is blocked and the element can finish streaming.

- `gst_collect_pads_collect()` and `gst_collect_pads_collect_range()` can be used by elements that start a GstTask to drive the collect_pads. This feature is however not yet implemented.

Last reviewed on 2006-05-10 (0.10.6)

## Details

### GstCollectData

    typedef struct {
      /* with LOCK of @collect */
      GstCollectPads        *collect;
      GstPad                *pad;
      GstBuffer             *buffer;
      guint                  pos;
      GstSegment             segment;
    } GstCollectData;

Structure used by the collect_pads.

GstCollectPads *`collect`; | owner GstCollectPads
GstPad *`pad`; | GstPad managed by this data
GstBuffer *`buffer`; | currently queued buffer.
guint `pos`; | position in the buffer
GstSegment `segment`; | last segment received.

### GstCollectPads

    typedef struct {
      GSList        *data;                  /* list of CollectData items */
    } GstCollectPads;

Collectpads object. Note that `data` doesn't contain the complete GstCollectData list at all times and should not be used for iterating them.

GSList *`data`; | GList of GstCollectData managed by this GstCollectPads.

### GstCollectPadsFunction ()

    GstFlowReturn       (*GstCollectPadsFunction)           (GstCollectPads *pads,
                                                             gpointer user_data);

A function that will be called when all pads have received data.

`pads` : | the GstCollectPads that triggered the callback
`user_data` : | user data passed to `gst_collect_pads_set_function()`
Returns : | GST_FLOW_OK for success

### GstCollectPadsClipFunction ()

    GstBuffer *         (*GstCollectPadsClipFunction)       (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             GstBuffer *buffer,
                                                             gpointer user_data);

A function that will be called when `buffer` is received on the pad managed by `data` in the collecpad object `pads`.

The function should use the segment of `data` and the negotiated media type on the pad to perform clipping of `buffer`.

This function takes ownership of `buffer`.

`pads` : | a GstCollectPads
`data` : | a GstCollectData
`buffer` : | a GstBuffer
`user_data` : | user data
Returns : | a GstBuffer that contains the clipped data of `buffer` or NULL when the buffer has been clipped completely.

Since 0.10.26

### GstCollectDataDestroyNotify ()

    void                (*GstCollectDataDestroyNotify)      (GstCollectData *data);

A function that will be called when the GstCollectData will be freed. It is passed the pointer to the structure and should free any custom memory and resources allocated for it.

`data` : | the GstCollectData that will be freed

Since 0.10.12

### gst_collect_pads_new ()

    GstCollectPads*     gst_collect_pads_new                (void);

Create a new instance of GstCollectPads.

Returns : | a new GstCollectPads, or NULL in case of an error. MT safe.

### gst_collect_pads_set_function ()

    void                gst_collect_pads_set_function       (GstCollectPads *pads,
                                                             GstCollectPadsFunction func,
                                                             gpointer user_data);

Set the callback function and user data that will be called when all the pads added to the collection have buffers queued.

MT safe.

`pads` : | the collectspads to use
`func` : | the function to set
`user_data` : | user data passed to the function

### gst_collect_pads_set_clip_function ()

    void                gst_collect_pads_set_clip_function  (GstCollectPads *pads,
                                                             GstCollectPadsClipFunction clipfunc,
                                                             gpointer user_data);

Install a clipping function that is called right after a buffer is received on a pad managed by `pads`. See GstCollectDataClipFunction for more info.

`pads` : | the collectspads to use
`clipfunc` : | clip function to install
`user_data` : | user data to pass to `clip_func`

Since 0.10.26

### gst_collect_pads_add_pad ()

    GstCollectData*     gst_collect_pads_add_pad            (GstCollectPads *pads,
                                                             GstPad *pad,
                                                             guint size);

Add a pad to the collection of collect pads. The pad has to be a sinkpad. The refcount of the pad is incremented. Use `gst_collect_pads_remove_pad()` to remove the pad from the collection again.

This function will override the chain and event functions of the pad along with the element_private data, which is used to store private information for the collectpads.

You specify a size for the returned GstCollectData structure so that you can use it to store additional information.

The pad will be automatically activated in push mode when `pads` is started.

This function calls `gst_collect_pads_add_pad_full()` passing a value of NULL for destroy_notify.

`pads` : | the collectspads to use
`pad` : | the pad to add
`size` : | the size of the returned GstCollectData structure
Returns : | a new GstCollectData to identify the new pad. Or NULL if wrong parameters are supplied. MT safe.

### gst_collect_pads_add_pad_full ()

    GstCollectData*     gst_collect_pads_add_pad_full       (GstCollectPads *pads,
                                                             GstPad *pad,
                                                             guint size,
                                                             GstCollectDataDestroyNotify destroy_notify);

Add a pad to the collection of collect pads. The pad has to be a sinkpad. The refcount of the pad is incremented. Use `gst_collect_pads_remove_pad()` to remove the pad from the collection again.

You specify a size for the returned GstCollectData structure so that you can use it to store additional information.

You can also specify a GstCollectDataDestroyNotify that will be called just before the GstCollectData structure is freed. It is passed the pointer to the structure and should free any custom memory and resources allocated for it.

The pad will be automatically activated in push mode when `pads` is started.

`pads` : | the collectspads to use
`pad` : | the pad to add
`size` : | the size of the returned GstCollectData structure
`destroy_notify` : | function to be called before the returned GstCollectData structure is freed
Returns : | a new GstCollectData to identify the new pad. Or NULL if wrong parameters are supplied. MT safe.

Since 0.10.12

### gst_collect_pads_remove_pad ()

    gboolean            gst_collect_pads_remove_pad         (GstCollectPads *pads,
                                                             GstPad *pad);

Remove a pad from the collection of collect pads. This function will also free the GstCollectData and all the resources that were allocated with `gst_collect_pads_add_pad()`.

The pad will be deactivated automatically when `pads` is stopped.

`pads` : | the collectspads to use
`pad` : | the pad to remove
Returns : | `TRUE` if the pad could be removed. MT safe.

### gst_collect_pads_is_active ()

    gboolean            gst_collect_pads_is_active          (GstCollectPads *pads,
                                                             GstPad *pad);

Check if a pad is active.

This function is currently not implemented.

`pads` : | the collectspads to use
`pad` : | the pad to check
Returns : | `TRUE` if the pad is active. MT safe.

### gst_collect_pads_collect ()

    GstFlowReturn       gst_collect_pads_collect            (GstCollectPads *pads);

Collect data on all pads. This function is usually called from a GstTask function in an element.

This function is currently not implemented.

`pads` : | the collectspads to use
Returns : | GstFlowReturn of the operation. MT safe.

### gst_collect_pads_collect_range ()

    GstFlowReturn       gst_collect_pads_collect_range      (GstCollectPads *pads,
                                                             guint64 offset,
                                                             guint length);

Collect data with `offset` and `length` on all pads. This function is typically called in the getrange function of an element.

This function is currently not implemented.

`pads` : | the collectspads to use
`offset` : | the offset to collect
`length` : | the length to collect
Returns : | GstFlowReturn of the operation. MT safe.

### gst_collect_pads_start ()

    void                gst_collect_pads_start              (GstCollectPads *pads);

Starts the processing of data in the collect_pads.

MT safe.

`pads` : | the collectspads to use

### gst_collect_pads_stop ()

    void                gst_collect_pads_stop               (GstCollectPads *pads);

Stops the processing of data in the collect_pads. this function will also unblock any blocking operations.

MT safe.

`pads` : | the collectspads to use

### gst_collect_pads_set_flushing ()

    void                gst_collect_pads_set_flushing       (GstCollectPads *pads,
                                                             gboolean flushing);

Change the flushing state of all the pads in the collection. No pad is able to accept anymore data when `flushing` is `TRUE`. Calling this function with `flushing` `FALSE` makes `pads` accept data again.

MT safe.

`pads` : | the collectspads to use
`flushing` : | desired state of the pads

Since 0.10.7.

### gst_collect_pads_peek ()

    GstBuffer*          gst_collect_pads_peek               (GstCollectPads *pads,
                                                             GstCollectData *data);

Peek at the buffer currently queued in `data`. This function should be called with the `pads` LOCK held, such as in the callback handler.

`pads` : | the collectspads to peek
`data` : | the data to use
Returns : | The buffer in `data` or NULL if no buffer is queued. should unref the buffer after usage. MT safe.

### gst_collect_pads_pop ()

    GstBuffer*          gst_collect_pads_pop                (GstCollectPads *pads,
                                                             GstCollectData *data);

Pop the buffer currently queued in `data`. This function should be called with the `pads` LOCK held, such as in the callback handler.

`pads` : | the collectspads to pop
`data` : | the data to use
Returns : | The buffer in `data` or NULL if no buffer was queued. You should unref the buffer after usage. MT safe.

### gst_collect_pads_available ()

    guint               gst_collect_pads_available          (GstCollectPads *pads);

Query how much bytes can be read from each queued buffer. This means that the result of this call is the maximum number of bytes that can be read from each of the pads.

This function should be called with `pads` LOCK held, such as in the callback.

`pads` : | the collectspads to query
Returns : | The maximum number of bytes queued on all pads. This function returns 0 if a pad has no queued buffer. MT safe.

### gst_collect_pads_read ()

    guint               gst_collect_pads_read               (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint8 **bytes,
                                                             guint size);

Get a pointer in `bytes` where `size` bytes can be read from the given pad `data`.

This function should be called with `pads` LOCK held, such as in the callback.

`pads` : | the collectspads to query
`data` : | the data to use
`bytes` : | a pointer to a byte array
`size` : | the number of bytes to read
Returns : | The number of bytes available for consumption in the memory pointed to by `bytes`. This can be less than `size` and is 0 if the pad is end-of-stream. MT safe.

### gst_collect_pads_read_buffer ()

    GstBuffer *         gst_collect_pads_read_buffer        (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint size);

Get a buffer of `size` bytes from the given pad `data`.

This function should be called with `pads` LOCK held, such as in the callback.

`pads` : | the collectspads to query
`data` : | the data to use
`size` : | the number of bytes to read
Returns : | A GstBuffer. The size of the buffer can be less that requested. A return of NULL signals that the pad is end-of-stream. Unref the buffer after use. MT safe.

Since 0.10.18

### gst_collect_pads_take_buffer ()

    GstBuffer *         gst_collect_pads_take_buffer        (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint size);

Get a buffer of `size` bytes from the given pad `data`. Flushes the amount of read bytes.

This function should be called with `pads` LOCK held, such as in the callback.

`pads` : | the collectspads to query
`data` : | the data to use
`size` : | the number of bytes to read
Returns : | A GstBuffer. The size of the buffer can be less that requested. A return of NULL signals that the pad is end-of-stream. Unref the buffer after use. MT safe.

Since 0.10.18

### gst_collect_pads_flush ()

    guint               gst_collect_pads_flush              (GstCollectPads *pads,
                                                             GstCollectData *data,
                                                             guint size);

Flush `size` bytes from the pad `data`.

This function should be called with `pads` LOCK held, such as in the callback.

`pads` : | the collectspads to query
`data` : | the data to use
`size` : | the number of bytes to flush
Returns : | The number of bytes flushed. This can be less than `size` and is 0 if the pad was end-of-stream. MT safe.