Get the next item from the iterator in elem.
Only when this function returns GST_ITERATOR_OK, elem will contain a valid
value. elem must have been initialized to the type of the iterator or
initialized to zeroes with g_value_unset(). The caller is responsible for
unsetting or resetting elem with g_value_unset() or g_value_reset()
after usage.
When this function returns GST_ITERATOR_DONE, no more elements can be
retrieved from it.
A return value of GST_ITERATOR_RESYNC indicates that the element list was
concurrently updated. The user of it should call gst_iterator_resync() to
get the newly updated list.
A return value of GST_ITERATOR_ERROR indicates an unrecoverable fatal error.
Get the next item from the iterator in elem. Only when this function returns GST_ITERATOR_OK, elem will contain a valid value. elem must have been initialized to the type of the iterator or initialized to zeroes with g_value_unset(). The caller is responsible for unsetting or resetting elem with g_value_unset() or g_value_reset() after usage. When this function returns GST_ITERATOR_DONE, no more elements can be retrieved from it. A return value of GST_ITERATOR_RESYNC indicates that the element list was concurrently updated. The user of it should call gst_iterator_resync() to get the newly updated list. A return value of GST_ITERATOR_ERROR indicates an unrecoverable fatal error.