1 .. -*- coding: utf-8; mode: rst -*-
3 .. _VIDIOC_ENCODER_CMD:
5 ************************************************
6 ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD
7 ************************************************
12 VIDIOC_ENCODER_CMD - VIDIOC_TRY_ENCODER_CMD - Execute an encoder command
18 .. c:function:: int ioctl( int fd, VIDIOC_ENCODER_CMD, struct v4l2_encoder_cmd *argp )
19 :name: VIDIOC_ENCODER_CMD
21 .. c:function:: int ioctl( int fd, VIDIOC_TRY_ENCODER_CMD, struct v4l2_encoder_cmd *argp )
22 :name: VIDIOC_TRY_ENCODER_CMD
29 File descriptor returned by :ref:`open() <func-open>`.
37 These ioctls control an audio/video (usually MPEG-) encoder.
38 ``VIDIOC_ENCODER_CMD`` sends a command to the encoder,
39 ``VIDIOC_TRY_ENCODER_CMD`` can be used to try a command without actually
42 To send a command applications must initialize all fields of a struct
43 :ref:`v4l2_encoder_cmd <v4l2-encoder-cmd>` and call
44 ``VIDIOC_ENCODER_CMD`` or ``VIDIOC_TRY_ENCODER_CMD`` with a pointer to
47 The ``cmd`` field must contain the command code. The ``flags`` field is
48 currently only used by the STOP command and contains one bit: If the
49 ``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag is set, encoding will continue
50 until the end of the current *Group Of Pictures*, otherwise it will stop
53 A :ref:`read() <func-read>` or :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`
54 call sends an implicit START command to the encoder if it has not been
55 started yet. After a STOP command, :ref:`read() <func-read>` calls will read
56 the remaining data buffered by the driver. When the buffer is empty,
57 :ref:`read() <func-read>` will return zero and the next :ref:`read() <func-read>`
58 call will restart the encoder.
60 A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
61 call of a streaming file descriptor sends an implicit immediate STOP to
62 the encoder, and all buffered data is discarded.
64 These ioctls are optional, not all drivers may support them. They were
65 introduced in Linux 2.6.21.
68 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
72 .. flat-table:: struct v4l2_encoder_cmd
84 - The encoder command, see :ref:`encoder-cmds`.
92 - Flags to go with the command, see :ref:`encoder-flags`. If no
93 flags are defined for this command, drivers and applications must
94 set this field to zero.
102 - Reserved for future extensions. Drivers and applications must set
107 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
111 .. flat-table:: Encoder Commands
119 - ``V4L2_ENC_CMD_START``
123 - Start the encoder. When the encoder is already running or paused,
124 this command does nothing. No flags are defined for this command.
128 - ``V4L2_ENC_CMD_STOP``
132 - Stop the encoder. When the ``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag
133 is set, encoding will continue until the end of the current *Group
134 Of Pictures*, otherwise encoding will stop immediately. When the
135 encoder is already stopped, this command does nothing. mem2mem
136 encoders will send a ``V4L2_EVENT_EOS`` event when the last frame
137 has been encoded and all frames are ready to be dequeued and will
138 set the ``V4L2_BUF_FLAG_LAST`` buffer flag on the last buffer of
139 the capture queue to indicate there will be no new buffers
140 produced to dequeue. This buffer may be empty, indicated by the
141 driver setting the ``bytesused`` field to 0. Once the
142 ``V4L2_BUF_FLAG_LAST`` flag was set, the
143 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
144 but return an ``EPIPE`` error code.
148 - ``V4L2_ENC_CMD_PAUSE``
152 - Pause the encoder. When the encoder has not been started yet, the
153 driver will return an ``EPERM`` error code. When the encoder is
154 already paused, this command does nothing. No flags are defined
159 - ``V4L2_ENC_CMD_RESUME``
163 - Resume encoding after a PAUSE command. When the encoder has not
164 been started yet, the driver will return an ``EPERM`` error code. When
165 the encoder is already running, this command does nothing. No
166 flags are defined for this command.
169 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
173 .. flat-table:: Encoder Command Flags
181 - ``V4L2_ENC_CMD_STOP_AT_GOP_END``
185 - Stop encoding at the end of the current *Group Of Pictures*,
186 rather than immediately.
192 On success 0 is returned, on error -1 and the ``errno`` variable is set
193 appropriately. The generic error codes are described at the
194 :ref:`Generic Error Codes <gen-errors>` chapter.
197 The ``cmd`` field is invalid.
200 The application sent a PAUSE or RESUME command when the encoder was