gstreamer/libs/gst/base/gstadapter.c
Wim Taymans 006b34dc3f libs/gst/base/gstadapter.c: Add some docs.
Original commit message from CVS:
* libs/gst/base/gstadapter.c:
Add some docs.
2006-03-15 16:22:26 +00:00

383 lines
11 KiB
C

/* GStreamer
* Copyright (C) 2004 Benjamin Otte <otte@gnome.org>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/**
* SECTION:gstadapter
* @short_description: adapts incoming data on a sink pad into chunks of N bytes
*
* This class is for elements that receive buffers in an undesired size.
* While for example raw video contains one image per buffer, the same is not
* true for a lot of other formats, especially those that come directly from
* a file. So if you have undefined buffer sizes and require a specific size,
* this object is for you.
*
* An adapter is created with gst_adapter_new(). It can be freed again with
* g_object_unref().
*
* The theory of operation is like this: All buffers received are put
* into the adapter using gst_adapter_push() and the data is then read back
* in chunks of the desired size using gst_adapter_peek(). After the data is
* processed, it is freed using gst_adapter_flush().
*
* For example, a sink pad's chain function that needs to pass data to a library
* in 512-byte chunks could be implemented like this:
* <programlisting>
* static GstFlowReturn
* sink_pad_chain (GstPad *pad, GstBuffer *buffer)
* {
* MyElement *this;
* GstAdapter *adapter;
* GstFlowReturn ret = GST_FLOW_OK;
*
* // will give the element an extra ref; remember to drop it
* this = MY_ELEMENT (gst_pad_get_parent (pad));
* adapter = this->adapter;
*
* // put buffer into adapter
* gst_adapter_push (adapter, buffer);
* // while we can read out 512 bytes, process them
* while (gst_adapter_available (adapter) >= 512 && ret == GST_FLOW_OK) {
* // use flowreturn as an error value
* ret = my_library_foo (gst_adapter_peek (adapter, 512));
* gst_adapter_flush (adapter, 512);
* }
*
* gst_object_unref (this);
* return ret;
* }
* </programlisting>
* For another example, a simple element inside GStreamer that uses GstAdapter
* is the libvisual element.
*
* An element using GstAdapter in its sink pad chain function should ensure that
* when the FLUSH_STOP event is received, that any queued data is cleared using
* gst_adapter_clear(). Data should also be cleared or processed on EOS and
* when changing state from #GST_STATE_PAUSED to #GST_STATE_READY.
*
* Also check the GST_BUFFER_FLAG_DISCONT flag on the buffer. Some elements might
* need to clear the adapter after a discontinuity.
*
* A last thing to note is that while GstAdapter is pretty optimized,
* merging buffers still might be an operation that requires a memcpy()
* operation, and this operation is not the fastest. Because of this, some
* functions like gst_adapter_available_fast() are provided to help speed up
* such cases should you want to.
*
* GstAdapter is not MT safe. All operations on an adapter must be serialized by
* the caller. This is not normally a problem, however, as the normal use case
* of GstAdapter is inside one pad's chain function, in which case access is
* serialized via the pad's STREAM_LOCK.
*
* Note that gst_adapter_push() takes ownership of the buffer passed. Use
* gst_buffer_ref() before pushing it into the adapter if you still want to
* access the buffer later. The adapter will never modify the data in the
* buffer pushed in it.
*
* Last reviewed on 2006-03-07 (0.10.4).
*/
#include <string.h>
#include "gstadapter.h"
/* default size for the assembled data buffer */
#define DEFAULT_SIZE 16
GST_DEBUG_CATEGORY_STATIC (gst_adapter_debug);
#define GST_CAT_DEFAULT gst_adapter_debug
#define _do_init(thing) \
GST_DEBUG_CATEGORY_INIT (gst_adapter_debug, "adapter", 0, "object to splice and merge buffers to desired size")
GST_BOILERPLATE_FULL (GstAdapter, gst_adapter, GObject, G_TYPE_OBJECT,
_do_init);
static void gst_adapter_dispose (GObject * object);
static void gst_adapter_finalize (GObject * object);
static void
gst_adapter_base_init (gpointer g_class)
{
/* nop */
}
static void
gst_adapter_class_init (GstAdapterClass * klass)
{
GObjectClass *object = G_OBJECT_CLASS (klass);
object->dispose = gst_adapter_dispose;
object->finalize = gst_adapter_finalize;
}
static void
gst_adapter_init (GstAdapter * adapter, GstAdapterClass * g_class)
{
adapter->assembled_data = g_malloc (DEFAULT_SIZE);
adapter->assembled_size = DEFAULT_SIZE;
}
static void
gst_adapter_dispose (GObject * object)
{
GstAdapter *adapter = GST_ADAPTER (object);
gst_adapter_clear (adapter);
GST_CALL_PARENT (G_OBJECT_CLASS, dispose, (object));
}
static void
gst_adapter_finalize (GObject * object)
{
GstAdapter *adapter = GST_ADAPTER (object);
g_free (adapter->assembled_data);
GST_CALL_PARENT (G_OBJECT_CLASS, finalize, (object));
}
/**
* gst_adapter_new:
*
* Creates a new #GstAdapter. Free with g_object_unref().
*
* Returns: a new #GstAdapter
*/
GstAdapter *
gst_adapter_new (void)
{
return g_object_new (GST_TYPE_ADAPTER, NULL);
}
/**
* gst_adapter_clear:
* @adapter: a #GstAdapter
*
* Removes all buffers from @adapter.
*/
void
gst_adapter_clear (GstAdapter * adapter)
{
g_return_if_fail (GST_IS_ADAPTER (adapter));
g_slist_foreach (adapter->buflist, (GFunc) gst_mini_object_unref, NULL);
g_slist_free (adapter->buflist);
adapter->buflist = NULL;
adapter->size = 0;
adapter->skip = 0;
adapter->assembled_len = 0;
}
/**
* gst_adapter_push:
* @adapter: a #GstAdapter
* @buf: a #GstBuffer to add to queue in the adapter
*
* Adds the data from @buf to the data stored inside @adapter and takes
* ownership of the buffer.
*/
void
gst_adapter_push (GstAdapter * adapter, GstBuffer * buf)
{
g_return_if_fail (GST_IS_ADAPTER (adapter));
g_return_if_fail (GST_IS_BUFFER (buf));
adapter->size += GST_BUFFER_SIZE (buf);
adapter->buflist = g_slist_append (adapter->buflist, buf);
}
/**
* gst_adapter_peek:
* @adapter: a #GstAdapter
* @size: the number of bytes to peek
*
* Gets the first @size bytes stored in the @adapter. The returned pointer is
* valid until the next function is called on the adapter.
*
* Note that setting the returned pointer as the data of a #GstBuffer is
* incorrect for general-purpose plugins. The reason is that if a downstream
* element stores the buffer so that it has access to it outside of the bounds
* of its chain function, the buffer will have an invalid data pointer after
* your element flushes the bytes. In that case you should use
* gst_adapter_take(), which returns a freshly-allocated buffer that you can set
* as #GstBuffer malloc_data.
*
* Returns #NULL if @size bytes are not available.
*
* Returns: a pointer to the first @size bytes of data, or NULL.
*/
const guint8 *
gst_adapter_peek (GstAdapter * adapter, guint size)
{
GstBuffer *cur;
GSList *cur_list;
guint copied;
g_return_val_if_fail (GST_IS_ADAPTER (adapter), NULL);
g_return_val_if_fail (size > 0, NULL);
/* we don't have enough data, return NULL */
if (size > adapter->size)
return NULL;
/* we have enough assembled data, return it */
if (adapter->assembled_len >= size)
return adapter->assembled_data;
/* our head buffer has enough data left, return it */
cur = adapter->buflist->data;
if (GST_BUFFER_SIZE (cur) >= size + adapter->skip)
return GST_BUFFER_DATA (cur) + adapter->skip;
if (adapter->assembled_size < size) {
adapter->assembled_size = (size / DEFAULT_SIZE + 1) * DEFAULT_SIZE;
GST_DEBUG_OBJECT (adapter, "setting size of internal buffer to %u",
adapter->assembled_size);
adapter->assembled_data =
g_realloc (adapter->assembled_data, adapter->assembled_size);
}
adapter->assembled_len = size;
copied = GST_BUFFER_SIZE (cur) - adapter->skip;
memcpy (adapter->assembled_data, GST_BUFFER_DATA (cur) + adapter->skip,
copied);
cur_list = g_slist_next (adapter->buflist);
while (copied < size) {
g_assert (cur_list);
cur = cur_list->data;
cur_list = g_slist_next (cur_list);
memcpy (adapter->assembled_data + copied, GST_BUFFER_DATA (cur),
MIN (GST_BUFFER_SIZE (cur), size - copied));
copied = MIN (size, copied + GST_BUFFER_SIZE (cur));
}
return adapter->assembled_data;
}
/**
* gst_adapter_flush:
* @adapter: a #GstAdapter
* @flush: the number of bytes to flush
*
* Flushes the first @flush bytes in the @adapter. The caller must ensure that
* at least this many bytes are available.
*
* See also: gst_adapter_peek().
*/
void
gst_adapter_flush (GstAdapter * adapter, guint flush)
{
GstBuffer *cur;
g_return_if_fail (GST_IS_ADAPTER (adapter));
g_return_if_fail (flush >= 0);
g_return_if_fail (flush <= adapter->size);
GST_LOG_OBJECT (adapter, "flushing %u bytes", flush);
adapter->size -= flush;
adapter->assembled_len = 0;
while (flush > 0) {
cur = adapter->buflist->data;
if (GST_BUFFER_SIZE (cur) <= flush + adapter->skip) {
/* can skip whole buffer */
flush -= GST_BUFFER_SIZE (cur) - adapter->skip;
adapter->skip = 0;
adapter->buflist = g_slist_remove (adapter->buflist, cur);
gst_buffer_unref (cur);
} else {
adapter->skip += flush;
break;
}
}
}
/**
* gst_adapter_take:
* @adapter: a #GstAdapter
* @nbytes: the number of bytes to take
*
* Returns a freshly allocated buffer containing the first @nbytes bytes of the
* @adapter. The returned bytes will be flushed from the adapter.
*
* Caller owns returned value. g_free after usage.
*
* Returns: oven-fresh hot data, or #NULL if @nbytes bytes are not available
*/
guint8 *
gst_adapter_take (GstAdapter * adapter, guint nbytes)
{
const guint8 *cdata;
guint8 *data;
g_return_val_if_fail (GST_IS_ADAPTER (adapter), NULL);
g_return_val_if_fail (nbytes > 0, NULL);
GST_LOG_OBJECT (adapter, "taking %u bytes", nbytes);
cdata = gst_adapter_peek (adapter, nbytes);
if (!cdata)
return NULL;
data = g_malloc (nbytes);
memcpy (data, cdata, nbytes);
gst_adapter_flush (adapter, nbytes);
return data;
}
/**
* gst_adapter_available:
* @adapter: a #GstAdapter
*
* Gets the maximum amount of bytes available, that is it returns the maximum
* value that can be supplied to gst_adapter_peek() without that function
* returning NULL.
*
* Returns: number of bytes available in @adapter
*/
guint
gst_adapter_available (GstAdapter * adapter)
{
g_return_val_if_fail (GST_IS_ADAPTER (adapter), 0);
return adapter->size;
}
/**
* gst_adapter_available_fast:
* @adapter: a #GstAdapter
*
* Gets the maximum number of bytes available without the need to do expensive
* operations (like copying the data into a temporary buffer).
*
* Returns: number of bytes available in @adapter without expensive operations
*/
guint
gst_adapter_available_fast (GstAdapter * adapter)
{
g_return_val_if_fail (GST_IS_ADAPTER (adapter), 0);
if (!adapter->buflist)
return 0;
if (adapter->assembled_len)
return adapter->assembled_len;
g_assert (GST_BUFFER_SIZE (adapter->buflist->data) > adapter->skip);
return GST_BUFFER_SIZE (adapter->buflist->data) - adapter->skip;
}