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Documents the protocol that user-space should follow when communicating with stateless video decoders. The stateless video decoding API makes use of the new request and tags APIs. While it has been implemented with the Cedrus driver so far, it should probably still be considered staging for a short while. Signed-off-by: Alexandre Courbot <acourbot@chromium.org> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
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2.2 KiB
ReStructuredText
50 lines
2.2 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/media/uapi/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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.. _mem2mem:
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********************************
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Video Memory-To-Memory Interface
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********************************
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A V4L2 memory-to-memory device can compress, decompress, transform, or
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otherwise convert video data from one format into another format, in memory.
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Such memory-to-memory devices set the ``V4L2_CAP_VIDEO_M2M`` or
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``V4L2_CAP_VIDEO_M2M_MPLANE`` capability. Examples of memory-to-memory
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devices are codecs, scalers, deinterlacers or format converters (i.e.
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converting from YUV to RGB).
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A memory-to-memory video node acts just like a normal video node, but it
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supports both output (sending frames from memory to the hardware)
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and capture (receiving the processed frames from the hardware into
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memory) stream I/O. An application will have to setup the stream I/O for
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both sides and finally call :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`
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for both capture and output to start the hardware.
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Memory-to-memory devices function as a shared resource: you can
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open the video node multiple times, each application setting up their
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own properties that are local to the file handle, and each can use
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it independently from the others. The driver will arbitrate access to
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the hardware and reprogram it whenever another file handler gets access.
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This is different from the usual video node behavior where the video
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properties are global to the device (i.e. changing something through one
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file handle is visible through another file handle).
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One of the most common memory-to-memory device is the codec. Codecs
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are more complicated than most and require additional setup for
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their codec parameters. This is done through codec controls.
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See :ref:`mpeg-controls`. More details on how to use codec memory-to-memory
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devices are given in the following sections.
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.. toctree::
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:maxdepth: 1
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dev-decoder
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dev-stateless-decoder
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