1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _mem2mem: 5 6******************************** 7Video Memory-To-Memory Interface 8******************************** 9 10A V4L2 memory-to-memory device can compress, decompress, transform, or 11otherwise convert video data from one format into another format, in memory. 12Such memory-to-memory devices set the ``V4L2_CAP_VIDEO_M2M`` or 13``V4L2_CAP_VIDEO_M2M_MPLANE`` capability. Examples of memory-to-memory 14devices are codecs, scalers, deinterlacers or format converters (i.e. 15converting from YUV to RGB). 16 17A memory-to-memory video node acts just like a normal video node, but it 18supports both output (sending frames from memory to the hardware) 19and capture (receiving the processed frames from the hardware into 20memory) stream I/O. An application will have to setup the stream I/O for 21both sides and finally call :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` 22for both capture and output to start the hardware. 23 24Memory-to-memory devices function as a shared resource: you can 25open the video node multiple times, each application setting up their 26own properties that are local to the file handle, and each can use 27it independently from the others. The driver will arbitrate access to 28the hardware and reprogram it whenever another file handler gets access. 29This is different from the usual video node behavior where the video 30properties are global to the device (i.e. changing something through one 31file handle is visible through another file handle). 32 33One of the most common memory-to-memory device is the codec. Codecs 34are more complicated than most and require additional setup for 35their codec parameters. This is done through codec controls. 36See :ref:`codec-controls`. More details on how to use codec memory-to-memory 37devices are given in the following sections. 38 39.. toctree:: 40 :maxdepth: 1 41 42 dev-decoder 43 dev-encoder 44 dev-stateless-decoder 45