mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-20 23:36:38 +00:00
212 lines
7.1 KiB
Text
212 lines
7.1 KiB
Text
STATUS: GstData is not implemented as a class for speed reasons.
|
|
----------------------------------------------------------------
|
|
|
|
NB: This document does not represent the current state of CVS but my current plans on how to implement this.
|
|
|
|
Basics
|
|
======
|
|
|
|
Hierarchy
|
|
---------
|
|
GstData
|
|
GstInstream
|
|
GstBuffer
|
|
GstEventNewMedia
|
|
GstEventDiscontinuous
|
|
GstEventEOS
|
|
GstEventLength
|
|
GstOutOfStream
|
|
GstEventLock
|
|
GstEventUnLock
|
|
GstEventSeek
|
|
GstEventFlush
|
|
GstEventEmpty
|
|
|
|
|
|
GstData
|
|
=======
|
|
|
|
typedef GstData * (*GstDataCopyFunction) (GstData *data);
|
|
typedef void (*GstDataFreeFunction) (GstData *data);
|
|
|
|
struct _GstData
|
|
{
|
|
/* is a */
|
|
GstDataClass * klass;
|
|
|
|
/* refcounting */
|
|
#ifdef HAVE_ATOMIC_H
|
|
atomic_t refcount;
|
|
#else
|
|
gint refcount;
|
|
GMutex * reflock;
|
|
#endif
|
|
|
|
/* flags */
|
|
guint flags;
|
|
};
|
|
|
|
struct _GstDataClass
|
|
{
|
|
GstDataType type;
|
|
|
|
GstDataCopyFunction copy;
|
|
GstDataFreeFunction free;
|
|
};
|
|
|
|
Inheritance
|
|
-----------
|
|
A GstData descandant GstMyData, would look like this:
|
|
struct _GstMyData {
|
|
GstData parent;
|
|
/* more stuff specific to GstMyData */
|
|
}
|
|
|
|
You can even enhance the class struct, if you want to. This works just like inheritance in GLib.
|
|
|
|
If it can be a parent class, it should implement these three functions publicly:
|
|
void gst_my_data_init (GstMyData *data) {
|
|
/* call the parent's init function, eg: */
|
|
gst_data_init (GST_DATA (data));
|
|
/* initialize your data now */
|
|
}
|
|
void gst_my_data_dispose (GstMyData *data) {
|
|
/* free every data, that needs to be freed */
|
|
/* call the parent's dispose function, eg: */
|
|
gst_data_dispose (GST_DATA (data));
|
|
/* do NOT free the data */
|
|
}
|
|
GstData *gst_my_data_do_copy (GstMyData *to, GstMyData *from) {
|
|
/* call the parent's copy function, eg: */
|
|
gst_data_do_copy (GST_DATA (to), GST_DATA (from));
|
|
/* copy relevant stuff from your struct now */
|
|
/* note: the copy function must return a writable object, you may not set GST_DATA_READONLY here */
|
|
}
|
|
|
|
If GstMyData should be instantiable, you should do this:
|
|
Get a class struct, something like this:
|
|
static GstDataClass my_data_class = { GST_TYPE_MY_DATA,
|
|
gst_my_data_copy_func,
|
|
gst_my_data_free_func };
|
|
FIXME: At the moment all types need to be specified in a big enum in gstdata.h.
|
|
We might want to change that when we support event plugins.
|
|
The two functions above should look something like this:
|
|
GstData *gst_my_data_copy_func (GstData *from) {
|
|
/* allocate memory */
|
|
GstMyData *copy = g_new (GstMyData, 1);
|
|
/* copy relevant variables or initialize them */
|
|
gst_my_data_copy (copy, GST_MY_DATA (from));
|
|
|
|
return copy;
|
|
}
|
|
void gst_my_data_free_func (GstData *data) {
|
|
/* first dispose all data */
|
|
gst_my_data_dispose (GST_MY_DATA (data));
|
|
/* now free the struct */
|
|
g_free (data);
|
|
}
|
|
|
|
Now you just need a function that can be called from the real world:
|
|
GstMyData *gst_my_data_new (void) {
|
|
/* allocate memory */
|
|
GstMyData *my_data = g_new (GstMyData, 1);
|
|
/* initialize the variables */
|
|
gst_my_data_init (my_data);
|
|
/* set the right type */
|
|
GST_DATA (my_data)->type = &my_data_class;
|
|
|
|
return my_data;
|
|
}
|
|
|
|
summary of inheritance:
|
|
- define structs like GObject inheritance
|
|
- inheritance works by calling the functions of the parent when creating/copying/freeing an object
|
|
- type recognition is done by the type field in the class struct
|
|
- memory allocation is specific to the struct.
|
|
|
|
Refcounting
|
|
-----------
|
|
GstData provides threadsafe refcounting. If you create a new object - either by copying or explicit creation - the refcount is initialized to 1.
|
|
This reference is owned by the creator of the object.
|
|
If the reference count reaches 0, the object is freed. The free function of the class is called for that purpose.
|
|
In accordance with GLib, that uses g_object_(un)ref for everything, gst_data_(un)ref is used and no wrapper macros are created.
|
|
|
|
MT safety
|
|
---------
|
|
Manipulating data inside an object is not threadsafe unless otherwise noted.
|
|
If an object has a reference count of 1 it is assumed that the reference holder is the only user of that object and he may modify it the way he likes.
|
|
If the reference count is greater than 1, the object may not be modified. If you need to modify it, you have to copy the object and use that copy instead.
|
|
NB: Object creation and refcounting are threadsafe - or must be implemented that way.
|
|
|
|
Flags
|
|
-----
|
|
Flags work and can be used like the GstObject flags.
|
|
GstData defines only one flag: GST_DATA_READONLY. If this flag is set, you are not allowed to modify the contents of a struct, even if the refcount is 1.
|
|
|
|
GBoxed
|
|
------
|
|
|
|
|
|
GstInstream
|
|
===========
|
|
|
|
GstInstream is the base class for events and buffers that are passed inside the stream.
|
|
It enhances the GstData struct by
|
|
guint64 offset[GST_OFFSET_TYPES];
|
|
This field describes the offset in the current stream in various different ways:
|
|
GST_OFFSET_BYTES: The number of bytes from the beginning of the stream.
|
|
GST_OFFSET_TIME: The timestamp in microseconds. The beginning of the stream equals timestamp 0. In buffers the timestamp should match the beginning of the data.
|
|
GST_OFFSET_FRAMES: This type is specific to the stream and should be defined there. (video will probably use it for frame numbers, audio to count samples)
|
|
If an offset can't be specified, it is set to GST_OFFSET_INVALID, which equals (guint64) -1. The byte offset always has to be specified. It is an error if it is invalid.
|
|
A plugin playing data from an "infinite" source (eg a shoutcast stream from the internet) it should start with byteoffset 0.
|
|
|
|
|
|
GstBuffer
|
|
=========
|
|
|
|
The buffer enhances the GstInstream struct by including a data and a size field.
|
|
|
|
Memory allocation
|
|
-----------------
|
|
Memory is allocated via a special memchunk implementation, that is threadsafe. The default implementation uses a mutex and GMemChunks.
|
|
FIXME: This is not true, we use g_malloc/g_free for now.
|
|
|
|
GstBufferClass
|
|
--------------
|
|
GstBufferClasses (note the plural) replace bufferpools. The default class uses g_free/g_malloc for storing data. However, you are free to write your own if
|
|
you need buffers that store data in another way.
|
|
Note however that the copy function needs to supply a writable copy of your buffer.
|
|
|
|
Subbuffers
|
|
----------
|
|
Subbuffers have been replaced by a special kind of GstBufferClass.
|
|
|
|
|
|
Instream events
|
|
===============
|
|
|
|
GstEventNewMedia
|
|
----------------
|
|
Signals the start of a new stream. This must be send before any buffer of a new stream can be send.
|
|
FIXME: The "must be send" can only be enforced if all elements are event aware. And this is necessary if we don't want to get parts of stream 1 inside stream 2.
|
|
|
|
GstEventDiscontinuous
|
|
---------------------
|
|
This must be send between buffers, that don't have continuous data. This is necessary for example after seeking or when data is dropped for speed.
|
|
|
|
GstEventEOS
|
|
-----------
|
|
Signals the end of a stream. Must be send after all data is finished. If you want to start a new stream, don't send this event, send a GstEventNewMedia instead.
|
|
After having processed this event, elements in the pipeline switch their state to paused.
|
|
|
|
GstEventLength
|
|
--------------
|
|
Specifies the length of the stream.
|
|
FIXME: Write more, when sure how to do this.
|
|
|
|
Upstream events
|
|
===============
|
|
These will be discussed in a separate doc.
|
|
|
|
|
|
|