media: docs-rst: Document memory-to-memory video encoder interface

    :maxdepth: 1

    dev-decoder

    dev-encoder

    dev-stateless-decoder

	inside the stream, when fed to a stateful mem2mem decoder, the fields

	may be zero to rely on the decoder to detect the right values. For more

	details see :ref:`decoder` and format descriptions.

	For compressed formats on the CAPTURE side of a stateful mem2mem

	encoder, the fields must be zero, since the coded size is expected to

	be calculated internally by the encoder itself, based on the OUTPUT

	side. For more details see :ref:`encoder` and format descriptions.

    * - __u32

      - ``pixelformat``

      - The pixel format or type of compression, set by the application.

- Figa, Tomasz <tfiga@chromium.org>

  - Documented the memory-to-memory decoder interface.

  - Documented the memory-to-memory encoder interface.

- H Schimek, Michael <mschimek@gmx.at>

- Osciak, Pawel <posciak@chromium.org>

  - Documented the memory-to-memory decoder interface.

  - Documented the memory-to-memory encoder interface.

- Osciak, Pawel <pawel@osciak.com>

``VIDIOC_ENCODER_CMD`` or ``VIDIOC_TRY_ENCODER_CMD`` with a pointer to

this structure.

The ``cmd`` field must contain the command code. The ``flags`` field is

currently only used by the STOP command and contains one bit: If the

``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag is set, encoding will continue

until the end of the current *Group Of Pictures*, otherwise it will stop

immediately.

The ``cmd`` field must contain the command code. Some commands use the

``flags`` field for additional information.

A :ref:`read() <func-read>` or :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`

call sends an implicit START command to the encoder if it has not been

started yet. After a STOP command, :ref:`read() <func-read>` calls will read

After a STOP command, :ref:`read() <func-read>` calls will read

the remaining data buffered by the driver. When the buffer is empty,

:ref:`read() <func-read>` will return zero and the next :ref:`read() <func-read>`

call will restart the encoder.

A :ref:`read() <func-read>` or :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`

call sends an implicit START command to the encoder if it has not been

started yet. Applies to both queues of mem2mem encoders.

A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`

call of a streaming file descriptor sends an implicit immediate STOP to

the encoder, and all buffered data is discarded.

the encoder, and all buffered data is discarded. Applies to both queues of

mem2mem encoders.

These ioctls are optional, not all drivers may support them. They were

introduced in Linux 2.6.21.

introduced in Linux 2.6.21. They are, however, mandatory for stateful mem2mem

encoders (as further documented in :ref:`encoder`).

.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|

      - 0

      - Start the encoder. When the encoder is already running or paused,

	this command does nothing. No flags are defined for this command.

	For a device implementing the :ref:`encoder`, once the drain sequence

	is initiated with the ``V4L2_ENC_CMD_STOP`` command, it must be driven

	to completion before this command can be invoked.  Any attempt to

	invoke the command while the drain sequence is in progress will trigger

	an ``EBUSY`` error code. See :ref:`encoder` for more details.

    * - ``V4L2_ENC_CMD_STOP``

      - 1

      - Stop the encoder. When the ``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag

	is set, encoding will continue until the end of the current *Group

	Of Pictures*, otherwise encoding will stop immediately. When the

	encoder is already stopped, this command does nothing. mem2mem

	encoders will send a ``V4L2_EVENT_EOS`` event when the last frame

	has been encoded and all frames are ready to be dequeued and will

	set the ``V4L2_BUF_FLAG_LAST`` buffer flag on the last buffer of

	the capture queue to indicate there will be no new buffers

	produced to dequeue. This buffer may be empty, indicated by the

	driver setting the ``bytesused`` field to 0. Once the

	``V4L2_BUF_FLAG_LAST`` flag was set, the

	:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,

	but return an ``EPIPE`` error code.

	encoder is already stopped, this command does nothing.

	For a device implementing the :ref:`encoder`, the command will initiate

	the drain sequence as documented in :ref:`encoder`. No flags or other

	arguments are accepted in this case. Any attempt to invoke the command

	again before the sequence completes will trigger an ``EBUSY`` error

	code.

    * - ``V4L2_ENC_CMD_PAUSE``

      - 2

      - Pause the encoder. When the encoder has not been started yet, the

      - Stop encoding at the end of the current *Group Of Pictures*,

	rather than immediately.

        Does not apply to :ref:`encoder`.

Return Value

============

appropriately. The generic error codes are described at the

:ref:`Generic Error Codes <gen-errors>` chapter.

EBUSY

    A drain sequence of a device implementing the :ref:`encoder` is still in

    progress. It is not allowed to issue another encoder command until it

    completes.

EINVAL

    The ``cmd`` field is invalid.