dev-mem2mem.rst (1903B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _mem2mem: 4 5******************************** 6Video Memory-To-Memory Interface 7******************************** 8 9A V4L2 memory-to-memory device can compress, decompress, transform, or 10otherwise convert video data from one format into another format, in memory. 11Such memory-to-memory devices set the ``V4L2_CAP_VIDEO_M2M`` or 12``V4L2_CAP_VIDEO_M2M_MPLANE`` capability. Examples of memory-to-memory 13devices are codecs, scalers, deinterlacers or format converters (i.e. 14converting from YUV to RGB). 15 16A memory-to-memory video node acts just like a normal video node, but it 17supports both output (sending frames from memory to the hardware) 18and capture (receiving the processed frames from the hardware into 19memory) stream I/O. An application will have to setup the stream I/O for 20both sides and finally call :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` 21for both capture and output to start the hardware. 22 23Memory-to-memory devices function as a shared resource: you can 24open the video node multiple times, each application setting up their 25own properties that are local to the file handle, and each can use 26it independently from the others. The driver will arbitrate access to 27the hardware and reprogram it whenever another file handler gets access. 28This is different from the usual video node behavior where the video 29properties are global to the device (i.e. changing something through one 30file handle is visible through another file handle). 31 32One of the most common memory-to-memory device is the codec. Codecs 33are more complicated than most and require additional setup for 34their codec parameters. This is done through codec controls. 35See :ref:`codec-controls`. More details on how to use codec memory-to-memory 36devices are given in the following sections. 37 38.. toctree:: 39 :maxdepth: 1 40 41 dev-decoder 42 dev-encoder 43 dev-stateless-decoder