doc/spec/x5953.htm

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Buffers</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REL="HOME"
TITLE="Video for Linux Two API Specification"
HREF="book1.htm"><LINK
REL="UP"
TITLE="Input/Output"
HREF="c5742.htm"><LINK
REL="PREVIOUS"
TITLE="Asynchronous I/O"
HREF="x5950.htm"><LINK
REL="NEXT"
TITLE="Field Order"
HREF="x6386.htm"></HEAD
><BODY
CLASS="SECTION"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Video for Linux Two API Specification: Revision 0.24</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x5950.htm"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 3. Input/Output</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x6386.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECTION"
><H1
CLASS="SECTION"
><A
NAME="BUFFER"
>3.5. Buffers</A
></H1
><P
>A buffer contains data exchanged by application and
driver using one of the Streaming I/O methods. Only pointers to
buffers are exchanged, the data itself is not copied. These pointers,
together with meta-information like timestamps or field parity, are
stored in a struct <CODE
CLASS="STRUCTNAME"
>v4l2_buffer</CODE
>, argument to
the <A
HREF="r13022.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_QUERYBUF</CODE
></A
>, <A
HREF="r12878.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_QBUF</CODE
></A
> and <A
HREF="r12878.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_DQBUF</CODE
></A
> ioctl.</P
><P
>Nominally timestamps refer to the first data byte transmitted.
In practice however the wide range of hardware covered by the V4L2 API
limits timestamp accuracy. Often an interrupt routine will
sample the system clock shortly after the field or frame was stored
completely in memory. So applications must expect a constant
difference up to one field or frame period plus a small (few scan
lines) random error. The delay and error can be much
larger due to compression or transmission over an external bus when
the frames are not properly stamped by the sender. This is frequently
the case with USB cameras. Here timestamps refer to the instant the
field or frame was received by the driver, not the capture time. These
devices identify by not enumerating any video standards, see <A
HREF="x448.htm"
>Section 1.7</A
>.</P
><P
>Similar limitations apply to output timestamps. Typically
the video hardware locks to a clock controlling the video timing, the
horizontal and vertical synchronization pulses. At some point in the
line sequence, possibly the vertical blanking, an interrupt routine
samples the system clock, compares against the timestamp and programs
the hardware to repeat the previous field or frame, or to display the
buffer contents.</P
><P
>Apart of limitations of the video device and natural
inaccuracies of all clocks, it should be noted system time itself is
not perfectly stable. It can be affected by power saving cycles,
warped to insert leap seconds, or even turned back or forth by the
system administrator affecting long term measurements. <A
NAME="AEN5967"
HREF="x5953.htm#FTN.AEN5967"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></P
><DIV
CLASS="TABLE"
><A
NAME="V4L2-BUFFER"
></A
><P
><B
>Table 3-1. struct <CODE
CLASS="STRUCTNAME"
>v4l2_buffer</CODE
></B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="20%"
TITLE="C1"><COL
WIDTH="20%"
TITLE="C2"><COL
WIDTH="20%"
TITLE="C3"><COL
WIDTH="40%"
TITLE="C4"><TBODY
VALIGN="TOP"
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>index</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Number of the buffer, set by the application. This
field is only used for <A
HREF="x5791.htm"
>memory mapping</A
> I/O
and can range from zero to the number of buffers allocated
with the <A
HREF="r13696.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_REQBUFS</CODE
></A
> ioctl (struct&nbsp;<A
HREF="r13696.htm#V4L2-REQUESTBUFFERS"
>v4l2_requestbuffers</A
> <CODE
CLASS="STRUCTFIELD"
>count</CODE
>) minus one.</TD
></TR
><TR
><TD
>enum&nbsp;<A
HREF="x5953.htm#V4L2-BUF-TYPE"
>v4l2_buf_type</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>type</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Type of the buffer, same as struct&nbsp;<A
HREF="r10944.htm#V4L2-FORMAT"
>v4l2_format</A
>
<CODE
CLASS="STRUCTFIELD"
>type</CODE
> or struct&nbsp;<A
HREF="r13696.htm#V4L2-REQUESTBUFFERS"
>v4l2_requestbuffers</A
>
<CODE
CLASS="STRUCTFIELD"
>type</CODE
>, set by the application.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>bytesused</CODE
></TD
><TD
>&nbsp;</TD
><TD
>The number of bytes occupied by the data in the
buffer. It depends on the negotiated data format and may change with
each buffer for compressed variable size data like JPEG images.
Drivers must set this field when <CODE
CLASS="STRUCTFIELD"
>type</CODE
>
refers to an input stream, applications when an output stream.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>flags</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Flags set by the application or driver, see <A
HREF="x5953.htm#BUFFER-FLAGS"
>Table 3-3</A
>.</TD
></TR
><TR
><TD
>enum&nbsp;<A
HREF="x6386.htm#V4L2-FIELD"
>v4l2_field</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>field</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Indicates the field order of the image in the
buffer, see <A
HREF="x6386.htm#V4L2-FIELD"
>Table 3-8</A
>. This field is not used when
the buffer contains VBI data. Drivers must set it when
<CODE
CLASS="STRUCTFIELD"
>type</CODE
> refers to an input stream,
applications when an output stream.</TD
></TR
><TR
><TD
>struct timeval</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>timestamp</CODE
></TD
><TD
>&nbsp;</TD
><TD
><P
>For input streams this is the
system time (as returned by the <CODE
CLASS="FUNCTION"
>gettimeofday()</CODE
>
function) when the first data byte was captured. For output streams
the data will not be displayed before this time, secondary to the
nominal frame rate determined by the current video standard in
enqueued order. Applications can for example zero this field to
display frames as soon as possible. The driver stores the time at
which the first data byte was actually sent out in the
<CODE
CLASS="STRUCTFIELD"
>timestamp</CODE
> field. This permits
applications to monitor the drift between the video and system
clock.</P
></TD
></TR
><TR
><TD
>struct&nbsp;<A
HREF="x5953.htm#V4L2-TIMECODE"
>v4l2_timecode</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>timecode</CODE
></TD
><TD
>&nbsp;</TD
><TD
>When <CODE
CLASS="STRUCTFIELD"
>type</CODE
> is
<CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VIDEO_CAPTURE</CODE
> and the
<CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_TIMECODE</CODE
> flag is set in
<CODE
CLASS="STRUCTFIELD"
>flags</CODE
>, this structure contains a frame
timecode. In <A
HREF="x6386.htm#V4L2-FIELD"
>V4L2_FIELD_ALTERNATE</A
>
mode the top and bottom field contain the same timecode.
Timecodes are intended to help video editing and are typically recorded on
video tapes, but also embedded in compressed formats like MPEG. This
field is independent of the <CODE
CLASS="STRUCTFIELD"
>timestamp</CODE
> and
<CODE
CLASS="STRUCTFIELD"
>sequence</CODE
> fields.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>sequence</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Set by the driver, counting the frames in the
sequence.</TD
></TR
><TR
><TD
COLSPAN="4"
><P
>In <A
HREF="x6386.htm#V4L2-FIELD"
>V4L2_FIELD_ALTERNATE</A
> mode the top and
bottom field have the same sequence number. The count starts at zero
and includes dropped or repeated frames. A dropped frame was received
by an input device but could not be stored due to lack of free buffer
space. A repeated frame was displayed again by an output device
because the application did not pass new data in
time.</P
><P
>Note this may count the frames received
e.g. over USB, without taking into account the frames dropped by the
remote hardware due to limited compression throughput or bus
bandwidth. These devices identify by not enumerating any video
standards, see <A
HREF="x448.htm"
>Section 1.7</A
>.</P
></TD
></TR
><TR
><TD
>enum&nbsp;<A
HREF="x5953.htm#V4L2-MEMORY"
>v4l2_memory</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>memory</CODE
></TD
><TD
>&nbsp;</TD
><TD
>This field must be set by applications and/or drivers
in accordance with the selected I/O method.</TD
></TR
><TR
><TD
>union</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>m</CODE
></TD
><TD
>&nbsp;</TD
><TD
>&nbsp;</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>offset</CODE
></TD
><TD
>When <CODE
CLASS="STRUCTFIELD"
>memory</CODE
> is
<CODE
CLASS="CONSTANT"
>V4L2_MEMORY_MMAP</CODE
> this is the offset of the buffer
from the start of the device memory. The value is returned by the
driver and apart of serving as parameter to the <A
HREF="r13889.htm"
><CODE
CLASS="FUNCTION"
>mmap()</CODE
></A
> function
not useful for applications. See <A
HREF="x5791.htm"
>Section 3.2</A
> for details.</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>unsigned long</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>userptr</CODE
></TD
><TD
>When <CODE
CLASS="STRUCTFIELD"
>memory</CODE
> is
<CODE
CLASS="CONSTANT"
>V4L2_MEMORY_USERPTR</CODE
> this is a pointer to the
buffer (casted to unsigned long type) in virtual memory, set by the
application. See <A
HREF="x5884.htm"
>Section 3.3</A
> for details.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>length</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Size of the buffer (not the payload) in bytes.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>input</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Some video capture drivers support rapid and
synchronous video input changes, a function useful for example in
video surveillance applications. For this purpose applications set the
<CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_INPUT</CODE
> flag, and this field to the
number of a video input as in struct&nbsp;<A
HREF="r8936.htm#V4L2-INPUT"
>v4l2_input</A
> field
<CODE
CLASS="STRUCTFIELD"
>index</CODE
>.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>reserved</CODE
></TD
><TD
>&nbsp;</TD
><TD
>A place holder for future extensions and custom
(driver defined) buffer types
<CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_PRIVATE</CODE
> and higher.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="V4L2-BUF-TYPE"
></A
><P
><B
>Table 3-2. enum v4l2_buf_type</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VIDEO_CAPTURE</CODE
></TD
><TD
>1</TD
><TD
>Buffer of a video capture stream, see <A
HREF="c6488.htm#CAPTURE"
>Section 4.1</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VIDEO_OUTPUT</CODE
></TD
><TD
>2</TD
><TD
>Buffer of a video output stream, see <A
HREF="x6831.htm"
>Section 4.3</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VIDEO_OVERLAY</CODE
></TD
><TD
>3</TD
><TD
>Buffer for video overlay, see <A
HREF="x6570.htm"
>Section 4.2</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VBI_CAPTURE</CODE
></TD
><TD
>4</TD
><TD
>Buffer of a raw VBI capture stream, see <A
HREF="x7013.htm"
>Section 4.7</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VBI_OUTPUT</CODE
></TD
><TD
>5</TD
><TD
>Buffer of a raw VBI output stream, see <A
HREF="x7013.htm"
>Section 4.7</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</CODE
></TD
><TD
>6</TD
><TD
>Buffer of a sliced VBI capture stream, see <A
HREF="x7236.htm"
>Section 4.8</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</CODE
></TD
><TD
>7</TD
><TD
>Buffer of a sliced VBI output stream, see <A
HREF="x7236.htm"
>Section 4.8</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY</CODE
></TD
><TD
>8</TD
><TD
>Buffer for video output overlay (OSD), see <A
HREF="x6909.htm"
>Section 4.4</A
>. Status: <A
HREF="x16453.htm"
>Experimental</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_TYPE_PRIVATE</CODE
></TD
><TD
>0x80</TD
><TD
>This and higher values are reserved for custom
(driver defined) buffer types.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="BUFFER-FLAGS"
></A
><P
><B
>Table 3-3. Buffer Flags</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_MAPPED</CODE
></TD
><TD
>0x0001</TD
><TD
>The buffer resides in device memory and has been mapped
into the application's address space, see <A
HREF="x5791.htm"
>Section 3.2</A
> for details.
Drivers set or clear this flag when the
<A
HREF="r13022.htm"
>VIDIOC_QUERYBUF</A
>, <A
HREF="r12878.htm"
>VIDIOC_QBUF</A
> or <A
HREF="r12878.htm"
>VIDIOC_DQBUF</A
> ioctl is called. Set by the driver.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_QUEUED</CODE
></TD
><TD
>0x0002</TD
><TD
>Internally drivers maintain two buffer queues, an
incoming and outgoing queue. When this flag is set, the buffer is
currently on the incoming queue. It automatically moves to the
outgoing queue after the buffer has been filled (capture devices) or
displayed (output devices). Drivers set or clear this flag when the
<CODE
CLASS="CONSTANT"
>VIDIOC_QUERYBUF</CODE
> ioctl is called. After
(successful) calling the <CODE
CLASS="CONSTANT"
>VIDIOC_QBUF </CODE
>ioctl it is
always set and after <CODE
CLASS="CONSTANT"
>VIDIOC_DQBUF</CODE
> always
cleared.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_DONE</CODE
></TD
><TD
>0x0004</TD
><TD
>When this flag is set, the buffer is currently on
the outgoing queue, ready to be dequeued from the driver. Drivers set
or clear this flag when the <CODE
CLASS="CONSTANT"
>VIDIOC_QUERYBUF</CODE
> ioctl
is called. After calling the <CODE
CLASS="CONSTANT"
>VIDIOC_QBUF</CODE
> or
<CODE
CLASS="CONSTANT"
>VIDIOC_DQBUF</CODE
> it is always cleared. Of course a
buffer cannot be on both queues at the same time, the
<CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_QUEUED</CODE
> and
<CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_DONE</CODE
> flag are mutually exclusive.
They can be both cleared however, then the buffer is in "dequeued"
state, in the application domain to say so.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_KEYFRAME</CODE
></TD
><TD
>0x0008</TD
><TD
>Drivers set or clear this flag when calling the
<CODE
CLASS="CONSTANT"
>VIDIOC_DQBUF</CODE
> ioctl. It may be set by video
capture devices when the buffer contains a compressed image which is a
key frame (or field), i.&nbsp;e. can be decompressed on its own.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_PFRAME</CODE
></TD
><TD
>0x0010</TD
><TD
>Similar to <CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_KEYFRAME</CODE
>
this flags predicted frames or fields which contain only differences to a
previous key frame.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_BFRAME</CODE
></TD
><TD
>0x0020</TD
><TD
>Similar to <CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_PFRAME</CODE
>
        this is a bidirectional predicted frame or field. [ooc tbd]</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_TIMECODE</CODE
></TD
><TD
>0x0100</TD
><TD
>The <CODE
CLASS="STRUCTFIELD"
>timecode</CODE
> field is valid.
Drivers set or clear this flag when the <CODE
CLASS="CONSTANT"
>VIDIOC_DQBUF</CODE
>
ioctl is called.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_BUF_FLAG_INPUT</CODE
></TD
><TD
>0x0200</TD
><TD
>The <CODE
CLASS="STRUCTFIELD"
>input</CODE
> field is valid.
Applications set or clear this flag before calling the
<CODE
CLASS="CONSTANT"
>VIDIOC_QBUF</CODE
> ioctl.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="V4L2-MEMORY"
></A
><P
><B
>Table 3-4. enum v4l2_memory</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_MEMORY_MMAP</CODE
></TD
><TD
>1</TD
><TD
>The buffer is used for <A
HREF="x5791.htm"
>memory
mapping</A
> I/O.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_MEMORY_USERPTR</CODE
></TD
><TD
>2</TD
><TD
>The buffer is used for <A
HREF="x5884.htm"
>user
pointer</A
> I/O.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_MEMORY_OVERLAY</CODE
></TD
><TD
>3</TD
><TD
>[to do]</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN6266"
>3.5.1. Timecodes</A
></H2
><P
>The <CODE
CLASS="STRUCTNAME"
>v4l2_timecode</CODE
> structure is
designed to hold a <A
HREF="b17127.htm#SMPTE12M"
><ABBR
CLASS="ABBREV"
>SMPTE&nbsp;12M</ABBR
></A
> or similar timecode.
(struct <CODE
CLASS="STRUCTNAME"
>timeval</CODE
> timestamps are stored in
struct&nbsp;<A
HREF="x5953.htm#V4L2-BUFFER"
>v4l2_buffer</A
> field <CODE
CLASS="STRUCTFIELD"
>timestamp</CODE
>.)</P
><DIV
CLASS="TABLE"
><A
NAME="V4L2-TIMECODE"
></A
><P
><B
>Table 3-5. struct <CODE
CLASS="STRUCTNAME"
>v4l2_timecode</CODE
></B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="25%"
TITLE="C1"><COL
WIDTH="25%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>type</CODE
></TD
><TD
>Frame rate the timecodes are based on, see <A
HREF="x5953.htm#TIMECODE-TYPE"
>Table 3-6</A
>.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>flags</CODE
></TD
><TD
>Timecode flags, see <A
HREF="x5953.htm#TIMECODE-FLAGS"
>Table 3-7</A
>.</TD
></TR
><TR
><TD
>__u8</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>frames</CODE
></TD
><TD
>Frame count, 0 ... 23/24/29/49/59, depending on the
            type of timecode.</TD
></TR
><TR
><TD
>__u8</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>seconds</CODE
></TD
><TD
>Seconds count, 0 ... 59. This is a binary, not BCD number.</TD
></TR
><TR
><TD
>__u8</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>minutes</CODE
></TD
><TD
>Minutes count, 0 ... 59. This is a binary, not BCD number.</TD
></TR
><TR
><TD
>__u8</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>hours</CODE
></TD
><TD
>Hours count, 0 ... 29. This is a binary, not BCD number.</TD
></TR
><TR
><TD
>__u8</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>userbits</CODE
>[4]</TD
><TD
>The "user group" bits from the timecode.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="TIMECODE-TYPE"
></A
><P
><B
>Table 3-6. Timecode Types</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_TYPE_24FPS</CODE
></TD
><TD
>1</TD
><TD
>24 frames per second, i.&nbsp;e. film.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_TYPE_25FPS</CODE
></TD
><TD
>2</TD
><TD
>25 frames per second, i.&nbsp;e. PAL or SECAM video.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_TYPE_30FPS</CODE
></TD
><TD
>3</TD
><TD
>30 frames per second, i.&nbsp;e. NTSC video.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_TYPE_50FPS</CODE
></TD
><TD
>4</TD
><TD
>&nbsp;</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_TYPE_60FPS</CODE
></TD
><TD
>5</TD
><TD
>&nbsp;</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="TIMECODE-FLAGS"
></A
><P
><B
>Table 3-7. Timecode Flags</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_FLAG_DROPFRAME</CODE
></TD
><TD
>0x0001</TD
><TD
>Indicates "drop frame" semantics for counting frames
in 29.97 fps material. When set, frame numbers 0 and 1 at the start of
each minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the
count.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_FLAG_COLORFRAME</CODE
></TD
><TD
>0x0002</TD
><TD
>The "color frame" flag.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_USERBITS_field</CODE
></TD
><TD
>0x000C</TD
><TD
>Field mask for the "binary group flags".</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_USERBITS_USERDEFINED</CODE
></TD
><TD
>0x0000</TD
><TD
>Unspecified format.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_TC_USERBITS_8BITCHARS</CODE
></TD
><TD
>0x0008</TD
><TD
>8-bit ISO characters.</TD
></TR
></TBODY
></TABLE
></DIV
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN5967"
HREF="x5953.htm#AEN5967"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Since no other Linux multimedia
API supports unadjusted time it would be foolish to introduce here. We
must use a universally supported clock to synchronize different media,
hence time of day.</P
></TD
></TR
></TABLE
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x5950.htm"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="book1.htm"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x6386.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Asynchronous I/O</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c5742.htm"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Field Order</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>