Buffers are the basic unit of data transfer in GStreamer. They contain the timing and offset along with other arbitrary metadata that is associated with the gstreamer.Memory blocks that the buffer contains.
Buffers are usually created with Buffer.new. After a buffer has been created one will typically allocate memory for it and add it to the buffer. The following example creates a buffer that can hold a given video frame with a given width, height and bits per plane.
1 2 GstBuffer *buffer; 3 GstMemory *memory; 4 gint size, width, height, bpp; 5 ... 6 size = width * height * bpp; 7 buffer = gst_buffer_new (); 8 memory = gst_allocator_alloc (NULL, size, NULL); 9 gst_buffer_insert_memory (buffer, -1, memory); 10 ...
Alternatively, use Buffer.newAllocate to create a buffer with preallocated data of a given size.
A buffer will usually have timestamps, and a duration, but neither of these are guaranteed (they may be set to GST_CLOCK_TIME_NONE). Whenever a meaningful value can be given for these, they should be set. The timestamps and duration are measured in nanoseconds (they are GstClockTime values).
The buffer DTS refers to the timestamp when the buffer should be decoded and is usually monotonically increasing. The buffer PTS refers to the timestamp when the buffer content should be presented to the user and is not always monotonically increasing.
A buffer can also have one or both of a start and an end offset. These are media-type specific. For video buffers, the start offset will generally be the frame number. For audio buffers, it will be the number of samples produced so far. For compressed data, it could be the byte offset in a source or destination file. Likewise, the end offset will be the offset of the end of the buffer. These can only be meaningfully interpreted if you know the media type of the buffer (the preceding CAPS event). Either or both can be set to GST_BUFFER_OFFSET_NONE
Buffer.ref is used to increase the refcount of a buffer. This must be done when you want to keep a handle to the buffer after pushing it to the next element. The buffer refcount determines the writability of the buffer, a buffer is only writable when the refcount is exactly 1, i.e. when the caller has the only reference to the buffer.
To efficiently create a smaller buffer out of an existing one, you can use Buffer.copyRegion. This method tries to share the memory objects between the two buffers.
If a plug-in wants to modify the buffer data or metadata in-place, it should first obtain a buffer that is safe to modify by using Buffer.makeWritable. This function is optimized so that a copy will only be made when it is necessary.
Several flags of the buffer can be set and unset with the GST_BUFFER_FLAG_SET() and GST_BUFFER_FLAG_UNSET() macros. Use GST_BUFFER_FLAG_IS_SET() to test if a certain GstBufferFlags flag is set.
Buffers can be efficiently merged into a larger buffer with Buffer.append. Copying of memory will only be done when absolutely needed.
Buffers are usually freed by unreffing them with Buffer.unref. When the refcount drops to 0, any memory and metadata pointed to by the buffer is unreffed as well. Buffers allocated from a gstreamer.BufferPool will be returned to the pool when the refcount drops to 0.
Typically, gstreamer.ParentBufferMeta is used when the child buffer is directly using the gstreamer.Memory of the parent buffer, and wants to prevent the parent buffer from being returned to a buffer pool until the gstreamer.Memory is available for re-use. (Since 1.6)
Sets our main struct and passes it to the parent class.
Creates a newly allocated buffer without any data.
Tries to create a newly allocated buffer with data of the given size and extra parameters from allocator. If the requested amount of memory can't be allocated, NULL will be returned. The allocated buffer memory is not cleared.
Creates a new buffer that wraps the given data. The memory will be freed with g_free and will be marked writable.
Allocate a new buffer that wraps the given memory. data must point to maxsize of memory, the wrapped buffer will have the region from offset and size visible.
Add metadata for info to buffer using the parameters in params.
Add a gstreamer.ParentBufferMeta to buffer that holds a reference on ref until the buffer is freed.
Attaches protection metadata to a gstreamer.Buffer
Append all the memory from buf2 to buf1. The result buffer will contain a concatenation of the memory of buf1 and buf2.
Append the memory block mem to buffer. This function takes ownership of mem and thus doesn't increase its refcount.
Append size bytes at offset from buf2 to buf1. The result buffer will contain a concatenation of the memory of buf1 and the requested region of buf2.
Create a copy of the given buffer. This will make a newly allocated copy of the data the source buffer contains.
Copies the information from src into dest.
Creates a sub-buffer from parent at offset and size. This sub-buffer uses the actual memory space of the parent buffer. This function will copy the offset and timestamp fields when the offset is 0. If not, they will be set to GST_CLOCK_TIME_NONE and GST_BUFFER_OFFSET_NONE
Copy size bytes starting from offset in buffer to dest.
Extracts a copy of at most size bytes the data at offset into newly-allocated memory. dest must be freed using g_free() when done.
Copy size bytes from src to buffer at offset.
Find the memory blocks that span size bytes starting from offset in buffer.
Call func with user_data for each meta in buffer.
Get all the memory block in buffer. The memory blocks will be merged into one large gstreamer.Memory
Get the main Gtk struct
Get the GstBufferFlags flags set on this buffer.
Get the memory block at index idx in buffer.
Get length memory blocks in buffer starting at idx. The memory blocks will be merged into one large gstreamer.Memory
Get the metadata for api on buffer. When there is no such metadata, NULL is returned. If multiple metadata with the given api are attached to this buffer only the first one is returned. To handle multiple metadata with a given API use Buffer.iterateMeta or Buffer.foreachMeta instead and check the meta->info.api member for the API type.
Find the first GstReferenceTimestampMeta on buffer that conforms to reference. Conformance is tested by checking if the meta's reference is a subset of reference.
Get the total size of the memory blocks in buffer.
Get the total size of the memory blocks in b.
Get the total size of length memory blocks stating from idx in buffer.
the main Gtk struct as a void*
Insert the memory block mem to buffer at idx. This function takes ownership of mem and thus doesn't increase its refcount.
Check if all memory blocks in buffer are writable.
Check if length memory blocks in buffer starting from idx are writable.
Retrieve the next GstMeta after current. If state points to NULL, the first metadata is returned.
Retrieve the next GstMeta of type meta_api_type after the current one according to state. If state points to NULL, the first metadata of type meta_api_type is returned.
This function fills info with the GstMapInfo of all merged memory blocks in buffer.
This function fills info with the GstMapInfo of length merged memory blocks starting at idx in buffer. When length is -1, all memory blocks starting from idx are merged and mapped.
Compare size bytes starting from offset in buffer with the memory in mem.
Fill buf with size bytes with val starting from offset.
Get the amount of memory blocks that this buffer has. This amount is never larger than what Buffer.getMaxMemory returns.
Get the memory block at idx in buffer. The memory block stays valid until the memory block in buffer is removed, replaced or merged, typically with any call that modifies the memory in buffer.
Prepend the memory block mem to buffer. This function takes ownership of mem and thus doesn't increase its refcount.
Remove all the memory blocks in buffer.
Remove the memory block in b at index i.
Remove length memory blocks in buffer starting from idx.
Remove the metadata for meta on buffer.
Replaces all memory in buffer with mem.
Replaces the memory block at index idx in buffer with mem.
Replaces length memory blocks in buffer starting at idx with mem.
Set the offset and total size of the memory blocks in buffer.
Set the total size of the length memory blocks starting at idx in buffer
Sets one or more buffer flags on a buffer.
Set the total size of the memory blocks in buffer.
Release the memory previously mapped with Buffer.map.
Clears one or more buffer flags.
Get the maximum amount of memory blocks that a buffer can hold. This is a compile time constant that can be queried with the function.
the main Gtk struct