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- .. -*- coding: utf-8; mode: rst -*-
- .. _codec:
- ***************
- Codec 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 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
- 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`.
- Memory-to-memory devices can often be used 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
- it independently from the others. The driver will arbitrate access to
- the codec 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).
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