gstreamer/docs/design/part-element-transform.txt

Transform elements
------------------

Transform elements transform input buffers to output buffers based
on the sink and source caps.

typical transform elements include:

 - audio convertors (audioconvert, ...)
 - video convertors (colorspace, videoscale, audioconvert, ...)
 - filters (capfilter, colorbalance, 

The implementation of the transform element has to take care of
the following things:

 - efficient negotiation both up and downstream
 - efficient buffer alloc and other buffer management

Some transform elements can operate in different modes:

 - passthrough (no changes to buffers)
 - in-place (changes made to incomming buffer)
 - metadata changes only 
 
Depending on the mode of operation the buffer allocation strategy might change.


Negotiation
-----------

The transform element is configured to perform a specific transform in these
two situations:

 - new caps are received on the sink pad.
 - new caps are received on the source pad when allocating an output buffer and
   we can transform to these caps with the current input buffer.
docs/design/part-element-transform.txt: Added some docs about the design of tranform elements. Original commit message from CVS: * docs/design/part-element-transform.txt: Added some docs about the design of tranform elements. * libs/gst/base/gstbasesrc.c: (gst_base_src_perform_seek), (gst_base_src_loop), (gst_base_src_change_state): Mark buffers with the DISCONT flag. 2006-03-08 13:44:55 +00:00			`Transform elements`
			`------------------`

			`Transform elements transform input buffers to output buffers based`
			`on the sink and source caps.`

			`typical transform elements include:`

			`- audio convertors (audioconvert, ...)`
			`- video convertors (colorspace, videoscale, audioconvert, ...)`
			`- filters (capfilter, colorbalance,`

			`The implementation of the transform element has to take care of`
			`the following things:`

			`- efficient negotiation both up and downstream`
			`- efficient buffer alloc and other buffer management`

			`Some transform elements can operate in different modes:`

			`- passthrough (no changes to buffers)`
			`- in-place (changes made to incomming buffer)`
			`- metadata changes only`

			`Depending on the mode of operation the buffer allocation strategy might change.`


			`Negotiation`
			`-----------`

			`The transform element is configured to perform a specific transform in these`
			`two situations:`

			`- new caps are received on the sink pad.`
			`- new caps are received on the source pad when allocating an output buffer and`
			`we can transform to these caps with the current input buffer.`