Commit 49179ff4 authored by Hans Verkuil's avatar Hans Verkuil Committed by Mauro Carvalho Chehab

media: Documentation/media: rename "Codec Interface"

The "Codec Interface" chapter is poorly named since codecs are just one
use-case of the Memory-to-Memory Interface. Rename it and clean up the
text a bit.
Signed-off-by: default avatarHans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: default avatarTomasz Figa <tfiga@chromium.org>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+samsung@kernel.org>
parent 0b7a4b41
......@@ -91,7 +91,7 @@ A request must contain at least one buffer, otherwise ``ENOENT`` is returned.
A queued request cannot be modified anymore.
.. caution::
For :ref:`memory-to-memory devices <codec>` you can use requests only for
For :ref:`memory-to-memory devices <mem2mem>` you can use requests only for
output buffers, not for capture buffers. Attempting to add a capture buffer
to a request will result in an ``EACCES`` error.
......@@ -152,7 +152,7 @@ if it had just been allocated.
Example for a Codec Device
--------------------------
For use-cases such as :ref:`codecs <codec>`, the request API can be used
For use-cases such as :ref:`codecs <mem2mem>`, the request API can be used
to associate specific controls to
be applied by the driver for the OUTPUT buffer, allowing user-space
to queue many such buffers in advance. It can also take advantage of requests'
......
......@@ -7,37 +7,36 @@
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
.. _codec:
.. _mem2mem:
***************
Codec Interface
***************
********************************
Video Memory-To-Memory Interface
********************************
A V4L2 codec can compress, decompress, transform, or otherwise convert
video data from one format into another format, in memory. Typically
such devices are memory-to-memory devices (i.e. devices with the
``V4L2_CAP_VIDEO_M2M`` or ``V4L2_CAP_VIDEO_M2M_MPLANE`` capability set).
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 codec hardware)
and capture (receiving the processed frames from the codec hardware into
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 codec.
Video compression codecs use the MPEG controls to setup their codec
parameters
.. note::
The MPEG controls actually support many more codecs than
just MPEG. See :ref:`mpeg-controls`.
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 codec properties that are local to the file handle, and each can use
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 codec and reprogram it whenever another file handler gets access.
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`.
......@@ -21,7 +21,7 @@ Interfaces
dev-overlay
dev-output
dev-osd
dev-codec
dev-mem2mem
dev-raw-vbi
dev-sliced-vbi
dev-radio
......
......@@ -73,7 +73,7 @@ Compressed Formats
- 'MG2S'
- MPEG-2 parsed slice data, as extracted from the MPEG-2 bitstream.
This format is adapted for stateless video decoders that implement a
MPEG-2 pipeline (using the :ref:`codec` and :ref:`media-request-api`).
MPEG-2 pipeline (using the :ref:`mem2mem` and :ref:`media-request-api`).
Metadata associated with the frame to decode is required to be passed
through the ``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS`` control and
quantization matrices can optionally be specified through the
......
......@@ -123,7 +123,7 @@ then ``EINVAL`` will be returned.
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` or calling :ref:`VIDIOC_REQBUFS`
the check for this will be reset.
For :ref:`memory-to-memory devices <codec>` you can specify the
For :ref:`memory-to-memory devices <mem2mem>` you can specify the
``request_fd`` only for output buffers, not for capture buffers. Attempting
to specify this for a capture buffer will result in an ``EACCES`` error.
......
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