mirror of https://gitee.com/openkylin/linux.git
198 lines
6.7 KiB
XML
198 lines
6.7 KiB
XML
<refentry id="vidioc-encoder-cmd">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_ENCODER_CMD</refname>
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<refname>VIDIOC_TRY_ENCODER_CMD</refname>
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<refpurpose>Execute an encoder command</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_encoder_cmd *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>These ioctls control an audio/video (usually MPEG-) encoder.
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<constant>VIDIOC_ENCODER_CMD</constant> sends a command to the
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encoder, <constant>VIDIOC_TRY_ENCODER_CMD</constant> can be used to
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try a command without actually executing it.</para>
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<para>To send a command applications must initialize all fields of a
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&v4l2-encoder-cmd; and call
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<constant>VIDIOC_ENCODER_CMD</constant> or
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<constant>VIDIOC_TRY_ENCODER_CMD</constant> with a pointer to this
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structure.</para>
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<para>The <structfield>cmd</structfield> field must contain the
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command code. The <structfield>flags</structfield> field is currently
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only used by the STOP command and contains one bit: If the
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<constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
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encoding will continue until the end of the current <wordasword>Group
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Of Pictures</wordasword>, otherwise it will stop immediately.</para>
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<para>A <function>read</function>() or &VIDIOC-STREAMON; call sends an implicit
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START command to the encoder if it has not been started yet. After a STOP command,
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<function>read</function>() calls will read the remaining data
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buffered by the driver. When the buffer is empty,
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<function>read</function>() will return zero and the next
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<function>read</function>() call will restart the encoder.</para>
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<para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
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file descriptor sends an implicit immediate STOP to the encoder, and all buffered
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data is discarded.</para>
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<para>These ioctls are optional, not all drivers may support
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them. They were introduced in Linux 2.6.21.</para>
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<table pgwide="1" frame="none" id="v4l2-encoder-cmd">
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<title>struct <structname>v4l2_encoder_cmd</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>cmd</structfield></entry>
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<entry>The encoder command, see <xref linkend="encoder-cmds" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Flags to go with the command, see <xref
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linkend="encoder-flags" />. If no flags are defined for
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this command, drivers and applications must set this field to
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zero.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>data</structfield>[8]</entry>
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<entry>Reserved for future extensions. Drivers and
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applications must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="encoder-cmds">
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<title>Encoder Commands</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_ENC_CMD_START</constant></entry>
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<entry>0</entry>
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<entry>Start the encoder. When the encoder is already
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running or paused, this command does nothing. No flags are defined for
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this command.</entry>
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</row>
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<row>
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<entry><constant>V4L2_ENC_CMD_STOP</constant></entry>
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<entry>1</entry>
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<entry>Stop the encoder. When the
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<constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
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encoding will continue until the end of the current <wordasword>Group
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Of Pictures</wordasword>, otherwise encoding will stop immediately.
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When the encoder is already stopped, this command does
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nothing. mem2mem encoders will send a <constant>V4L2_EVENT_EOS</constant> event
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when the last frame has been decoded and all frames are ready to be dequeued and
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will set the <constant>V4L2_BUF_FLAG_LAST</constant> buffer flag on the last
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buffer of the capture queue to indicate there will be no new buffers produced to
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dequeue. This buffer may be empty, indicated by the driver setting the
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<structfield>bytesused</structfield> field to 0. Once the
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<constant>V4L2_BUF_FLAG_LAST</constant> flag was set, the
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<link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl will not block anymore,
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but return an &EPIPE;.</entry>
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</row>
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<row>
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<entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>
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<entry>2</entry>
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<entry>Pause the encoder. When the encoder has not been
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started yet, the driver will return an &EPERM;. When the encoder is
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already paused, this command does nothing. No flags are defined for
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this command.</entry>
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</row>
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<row>
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<entry><constant>V4L2_ENC_CMD_RESUME</constant></entry>
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<entry>3</entry>
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<entry>Resume encoding after a PAUSE command. When the
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encoder has not been started yet, the driver will return an &EPERM;.
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When the encoder is already running, this command does nothing. No
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flags are defined for this command.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="encoder-flags">
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<title>Encoder Command Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant></entry>
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<entry>0x0001</entry>
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<entry>Stop encoding at the end of the current <wordasword>Group Of
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Pictures</wordasword>, rather than immediately.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The <structfield>cmd</structfield> field is invalid.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EPERM</errorcode></term>
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<listitem>
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<para>The application sent a PAUSE or RESUME command when
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the encoder was not running.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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