2005-11-09 Andy Wingo <wingo@pobox.com>
+ * gst/base/gstadapter.c: More adapter docs.
+
* gst/elements/gstfilesink.c (gst_file_sink_start)
(gst_file_sink_stop): New functions, replace the state change
handler.
/**
* SECTION:gstadapter
- * @short_description: object to splice and merge buffers to desired size
- * @see_also: #GstBytestream, #GstFilePad
+ * @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
* 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(). An example function that
- * needs to process data in 10 byte chunks could look like this:
+ * 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>
- * void
- * process_buffer (GstAdapter *adapter, GstBuffer *buffer)
+ * static GstFlowReturn
+ * sink_pad_chain (GstPad *pad, GstBuffer *buffer)
* {
- * guint8 *data;
+ * 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 10 bytes, process them
- * while ((data = #gst_adapter_peek (adapter, 10))) {
- * // process the 10 bytes here
- * // after processing the data, flush it
- * #gst_adapter_flush (adapter, 10);
+ * // while we can read out 512 bytes, process them
+ * while (#gst_adapter_available (adapter) >= 512 && fret == 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.
+ *
* 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.
+ *
+ * Last reviewed on 2005-11-08 (0.9.5).
*/
#include <string.h>
#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)
+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_dispose (GObject * object);
+static void gst_adapter_finalize (GObject * object);
- static void gst_adapter_base_init (gpointer g_class)
+static void
+gst_adapter_base_init (gpointer g_class)
{
+ /* nop */
}
static void
/**
* gst_adapter_clear:
- * @adapter: the #GstAdapter to clear
+ * @adapter: a #GstAdapter
*
- * Removes all buffers from the @adapter.
+ * Removes all buffers from @adapter.
*/
void
gst_adapter_clear (GstAdapter * adapter)
/**
* gst_adapter_peek:
* @adapter: a #GstAdapter
- * @size: number of bytes to peek
+ * @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.
*
- * Gets the first @size bytes stored in the @adapter. If this many bytes are
- * not available, it returns NULL. The returned pointer is valid until the next
- * function is called on the adapter.
+ * Returns #NULL if @size bytes are not available.
*
- * Returns: a pointer to the first @size bytes of data or NULL
+ * Returns: a pointer to the first @size bytes of data, or NULL.
*/
const guint8 *
gst_adapter_peek (GstAdapter * adapter, guint size)
/**
* gst_adapter_flush:
* @adapter: a #GstAdapter
- * @flush: number of bytes to flush
+ * @flush: the number of bytes to flush
*
- * Flushes the first @flush bytes of the @adapter.
+ * Flushes the first @flush bytes out of @adapter.
+ *
+ * See also: gst_adapter_peek().
*/
void
gst_adapter_flush (GstAdapter * adapter, guint flush)
/**
* gst_adapter_take:
* @adapter: a #GstAdapter
- * @nbytes: number of bytes to take
+ * @nbytes: the number of bytes to take
*
* Returns a freshly allocated buffer containing the first @nbytes bytes of the
- * @adapter. g_free() the return value after use.
+ * @adapter.
+ *
+ * Caller owns returned value.
*
- * Returns: oven-fresh hot data, or NULL if @nbytes bytes are not available
+ * Returns: oven-fresh hot data, or #NULL if @nbytes bytes are not available
*/
guint8 *
gst_adapter_take (GstAdapter * adapter, guint nbytes)
* value that can be supplied to gst_adapter_peek() without that function
* returning NULL.
*
- * Returns: amount of bytes available in @adapter
+ * Returns: number of bytes available in @adapter
*/
guint
gst_adapter_available (GstAdapter * adapter)
struct _GstAdapter {
GObject object;
+ /*< private >*/
GSList * buflist;
guint size;
guint skip;
guint assembled_size;
guint assembled_len;
- /*< private >*/
gpointer _gst_reserved[GST_PADDING];
};
/**
* SECTION:gstadapter
- * @short_description: object to splice and merge buffers to desired size
- * @see_also: #GstBytestream, #GstFilePad
+ * @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
* 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(). An example function that
- * needs to process data in 10 byte chunks could look like this:
+ * 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>
- * void
- * process_buffer (GstAdapter *adapter, GstBuffer *buffer)
+ * static GstFlowReturn
+ * sink_pad_chain (GstPad *pad, GstBuffer *buffer)
* {
- * guint8 *data;
+ * 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 10 bytes, process them
- * while ((data = #gst_adapter_peek (adapter, 10))) {
- * // process the 10 bytes here
- * // after processing the data, flush it
- * #gst_adapter_flush (adapter, 10);
+ * // while we can read out 512 bytes, process them
+ * while (#gst_adapter_available (adapter) >= 512 && fret == 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.
+ *
* 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.
+ *
+ * Last reviewed on 2005-11-08 (0.9.5).
*/
#include <string.h>
#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)
+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_dispose (GObject * object);
+static void gst_adapter_finalize (GObject * object);
- static void gst_adapter_base_init (gpointer g_class)
+static void
+gst_adapter_base_init (gpointer g_class)
{
+ /* nop */
}
static void
/**
* gst_adapter_clear:
- * @adapter: the #GstAdapter to clear
+ * @adapter: a #GstAdapter
*
- * Removes all buffers from the @adapter.
+ * Removes all buffers from @adapter.
*/
void
gst_adapter_clear (GstAdapter * adapter)
/**
* gst_adapter_peek:
* @adapter: a #GstAdapter
- * @size: number of bytes to peek
+ * @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.
*
- * Gets the first @size bytes stored in the @adapter. If this many bytes are
- * not available, it returns NULL. The returned pointer is valid until the next
- * function is called on the adapter.
+ * Returns #NULL if @size bytes are not available.
*
- * Returns: a pointer to the first @size bytes of data or NULL
+ * Returns: a pointer to the first @size bytes of data, or NULL.
*/
const guint8 *
gst_adapter_peek (GstAdapter * adapter, guint size)
/**
* gst_adapter_flush:
* @adapter: a #GstAdapter
- * @flush: number of bytes to flush
+ * @flush: the number of bytes to flush
*
- * Flushes the first @flush bytes of the @adapter.
+ * Flushes the first @flush bytes out of @adapter.
+ *
+ * See also: gst_adapter_peek().
*/
void
gst_adapter_flush (GstAdapter * adapter, guint flush)
/**
* gst_adapter_take:
* @adapter: a #GstAdapter
- * @nbytes: number of bytes to take
+ * @nbytes: the number of bytes to take
*
* Returns a freshly allocated buffer containing the first @nbytes bytes of the
- * @adapter. g_free() the return value after use.
+ * @adapter.
+ *
+ * Caller owns returned value.
*
- * Returns: oven-fresh hot data, or NULL if @nbytes bytes are not available
+ * Returns: oven-fresh hot data, or #NULL if @nbytes bytes are not available
*/
guint8 *
gst_adapter_take (GstAdapter * adapter, guint nbytes)
* value that can be supplied to gst_adapter_peek() without that function
* returning NULL.
*
- * Returns: amount of bytes available in @adapter
+ * Returns: number of bytes available in @adapter
*/
guint
gst_adapter_available (GstAdapter * adapter)
struct _GstAdapter {
GObject object;
+ /*< private >*/
GSList * buflist;
guint size;
guint skip;
guint assembled_size;
guint assembled_len;
- /*< private >*/
gpointer _gst_reserved[GST_PADDING];
};
projects / platform / upstream / gstreamer.git / commitdiff