mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-21 19:53:59 +08:00
059b1c5b15
SPDX v3.10 gained support for GFDL-1.1 with no invariant sections: https://spdx.org/licenses/GFDL-1.1-no-invariants-or-later.html So, remove the license text, replacing them by this new SPDX license. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
44 lines
1.9 KiB
ReStructuredText
44 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
|
|
|
|
.. _mem2mem:
|
|
|
|
********************************
|
|
Video Memory-To-Memory Interface
|
|
********************************
|
|
|
|
A V4L2 memory-to-memory device can compress, decompress, transform, or
|
|
otherwise convert video data from one format into another format, in memory.
|
|
Such memory-to-memory devices set the ``V4L2_CAP_VIDEO_M2M`` or
|
|
``V4L2_CAP_VIDEO_M2M_MPLANE`` capability. Examples of memory-to-memory
|
|
devices are codecs, scalers, deinterlacers or format converters (i.e.
|
|
converting from YUV to RGB).
|
|
|
|
A memory-to-memory video node acts just like a normal video node, but it
|
|
supports both output (sending frames from memory to the hardware)
|
|
and capture (receiving the processed frames from the hardware into
|
|
memory) stream I/O. An application will have to setup the stream I/O for
|
|
both sides and finally call :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`
|
|
for both capture and output to start the hardware.
|
|
|
|
Memory-to-memory devices function as a shared resource: you can
|
|
open the video node multiple times, each application setting up their
|
|
own properties that are local to the file handle, and each can use
|
|
it independently from the others. The driver will arbitrate access to
|
|
the hardware and reprogram it whenever another file handler gets access.
|
|
This is different from the usual video node behavior where the video
|
|
properties are global to the device (i.e. changing something through one
|
|
file handle is visible through another file handle).
|
|
|
|
One of the most common memory-to-memory device is the codec. Codecs
|
|
are more complicated than most and require additional setup for
|
|
their codec parameters. This is done through codec controls.
|
|
See :ref:`mpeg-controls`. More details on how to use codec memory-to-memory
|
|
devices are given in the following sections.
|
|
|
|
.. toctree::
|
|
:maxdepth: 1
|
|
|
|
dev-decoder
|
|
dev-encoder
|
|
dev-stateless-decoder
|