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[media] Add multi-planar API documentation

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Add DocBook documentation for the new multi-planar API extensions to the
Video for Linux 2 API DocBook.

Signed-off-by: Pawel Osciak <pawel@osciak.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Pawel Osciak 2011-01-07 01:41:33 -03:00 committed by Mauro Carvalho Chehab
parent c4c0a78d45
commit 53b5d5749b
16 changed files with 530 additions and 70 deletions
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4
Documentation/DocBook/media-entities.tmpl
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@ -129,6 +129,7 @@
<!ENTITY v4l2-audioout "struct&nbsp;<link linkend='v4l2-audioout'>v4l2_audioout</link>">
<!ENTITY v4l2-bt-timings "struct&nbsp;<link linkend='v4l2-bt-timings'>v4l2_bt_timings</link>">
<!ENTITY v4l2-buffer "struct&nbsp;<link linkend='v4l2-buffer'>v4l2_buffer</link>">
<!ENTITY v4l2-plane "struct&nbsp;<link linkend='v4l2-plane'>v4l2_plane</link>">
<!ENTITY v4l2-capability "struct&nbsp;<link linkend='v4l2-capability'>v4l2_capability</link>">
<!ENTITY v4l2-captureparm "struct&nbsp;<link linkend='v4l2-captureparm'>v4l2_captureparm</link>">
<!ENTITY v4l2-clip "struct&nbsp;<link linkend='v4l2-clip'>v4l2_clip</link>">
@ -167,6 +168,8 @@
<!ENTITY v4l2-output "struct&nbsp;<link linkend='v4l2-output'>v4l2_output</link>">
<!ENTITY v4l2-outputparm "struct&nbsp;<link linkend='v4l2-outputparm'>v4l2_outputparm</link>">
<!ENTITY v4l2-pix-format "struct&nbsp;<link linkend='v4l2-pix-format'>v4l2_pix_format</link>">
<!ENTITY v4l2-pix-format-mplane "struct&nbsp;<link linkend='v4l2-pix-format-mplane'>v4l2_pix_format_mplane</link>">
<!ENTITY v4l2-plane-pix-format "struct&nbsp;<link linkend='v4l2-plane-pix-format'>v4l2_plane_pix_format</link>">
<!ENTITY v4l2-queryctrl "struct&nbsp;<link linkend='v4l2-queryctrl'>v4l2_queryctrl</link>">
<!ENTITY v4l2-querymenu "struct&nbsp;<link linkend='v4l2-querymenu'>v4l2_querymenu</link>">
<!ENTITY v4l2-rect "struct&nbsp;<link linkend='v4l2-rect'>v4l2_rect</link>">
@ -202,6 +205,7 @@
<!-- Subsections -->
<!ENTITY sub-biblio SYSTEM "v4l/biblio.xml">
<!ENTITY sub-common SYSTEM "v4l/common.xml">
<!ENTITY sub-planar-apis SYSTEM "v4l/planar-apis.xml">
<!ENTITY sub-compat SYSTEM "v4l/compat.xml">
<!ENTITY sub-controls SYSTEM "v4l/controls.xml">
<!ENTITY sub-dev-capture SYSTEM "v4l/dev-capture.xml">

2
Documentation/DocBook/v4l/common.xml
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@ -846,6 +846,8 @@ conversion routine or library for integration into applications.</para>
</section>
</section>
&sub-planar-apis;
<section id="crop">
<title>Image Cropping, Insertion and Scaling</title>

11
Documentation/DocBook/v4l/compat.xml
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@ -2353,6 +2353,17 @@ that used it. It was originally scheduled for removal in 2.6.35.
</listitem>
</orderedlist>
</section>
<section>
<title>V4L2 in Linux 2.6.38</title>
<orderedlist>
<listitem>
<para>Multi-planar API added. Does not affect the compatibility of
current drivers and applications. See
<link linkend="planar-apis">multi-planar API</link>
for details.</para>
</listitem>
</orderedlist>
</section>
<section id="other">
<title>Relation of V4L2 to other Linux multimedia APIs</title>

13
Documentation/DocBook/v4l/dev-capture.xml
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@ -18,7 +18,8 @@ files are used for video output devices.</para>
<title>Querying Capabilities</title>
<para>Devices supporting the video capture interface set the
<constant>V4L2_CAP_VIDEO_CAPTURE</constant> flag in the
<constant>V4L2_CAP_VIDEO_CAPTURE</constant> or
<constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant> flag in the
<structfield>capabilities</structfield> field of &v4l2-capability;
returned by the &VIDIOC-QUERYCAP; ioctl. As secondary device functions
they may also support the <link linkend="overlay">video overlay</link>
@ -64,9 +65,11 @@ linkend="crop" />.</para>
<para>To query the current image format applications set the
<structfield>type</structfield> field of a &v4l2-format; to
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> and call the
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> or
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant> and call the
&VIDIOC-G-FMT; ioctl with a pointer to this structure. Drivers fill
the &v4l2-pix-format; <structfield>pix</structfield> member of the
the &v4l2-pix-format; <structfield>pix</structfield> or the
&v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member of the
<structfield>fmt</structfield> union.</para>
<para>To request different parameters applications set the
@ -84,8 +87,8 @@ adjust the parameters and finally return the actual parameters as
without disabling I/O or possibly time consuming hardware
preparations.</para>
<para>The contents of &v4l2-pix-format; are discussed in <xref
linkend="pixfmt" />. See also the specification of the
<para>The contents of &v4l2-pix-format; and &v4l2-pix-format-mplane;
are discussed in <xref linkend="pixfmt" />. See also the specification of the
<constant>VIDIOC_G_FMT</constant>, <constant>VIDIOC_S_FMT</constant>
and <constant>VIDIOC_TRY_FMT</constant> ioctls for details. Video
capture devices must implement both the

13
Documentation/DocBook/v4l/dev-output.xml
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@ -17,7 +17,8 @@ files are used for video capture devices.</para>
<title>Querying Capabilities</title>
<para>Devices supporting the video output interface set the
<constant>V4L2_CAP_VIDEO_OUTPUT</constant> flag in the
<constant>V4L2_CAP_VIDEO_OUTPUT</constant> or
<constant>V4L2_CAP_VIDEO_OUTPUT_MPLANE</constant> flag in the
<structfield>capabilities</structfield> field of &v4l2-capability;
returned by the &VIDIOC-QUERYCAP; ioctl. As secondary device functions
they may also support the <link linkend="raw-vbi">raw VBI
@ -60,9 +61,11 @@ linkend="crop" />.</para>
<para>To query the current image format applications set the
<structfield>type</structfield> field of a &v4l2-format; to
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> and call the
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> or
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant> and call the
&VIDIOC-G-FMT; ioctl with a pointer to this structure. Drivers fill
the &v4l2-pix-format; <structfield>pix</structfield> member of the
the &v4l2-pix-format; <structfield>pix</structfield> or the
&v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member of the
<structfield>fmt</structfield> union.</para>
<para>To request different parameters applications set the
@ -80,8 +83,8 @@ adjust the parameters and finally return the actual parameters as
without disabling I/O or possibly time consuming hardware
preparations.</para>
<para>The contents of &v4l2-pix-format; are discussed in <xref
linkend="pixfmt" />. See also the specification of the
<para>The contents of &v4l2-pix-format; and &v4l2-pix-format-mplane;
are discussed in <xref linkend="pixfmt" />. See also the specification of the
<constant>VIDIOC_G_FMT</constant>, <constant>VIDIOC_S_FMT</constant>
and <constant>VIDIOC_TRY_FMT</constant> ioctls for details. Video
output devices must implement both the

10
Documentation/DocBook/v4l/func-mmap.xml
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@ -45,7 +45,10 @@ just specify a <constant>NULL</constant> pointer here.</para>
<listitem>
<para>Length of the memory area to map. This must be the
same value as returned by the driver in the &v4l2-buffer;
<structfield>length</structfield> field.</para>
<structfield>length</structfield> field for the
single-planar API, and the same value as returned by the driver
in the &v4l2-plane; <structfield>length</structfield> field for the
multi-planar API.</para>
</listitem>
</varlistentry>
<varlistentry>
@ -106,7 +109,10 @@ flag.</para>
<listitem>
<para>Offset of the buffer in device memory. This must be the
same value as returned by the driver in the &v4l2-buffer;
<structfield>m</structfield> union <structfield>offset</structfield> field.</para>
<structfield>m</structfield> union <structfield>offset</structfield> field for
the single-planar API, and the same value as returned by the driver
in the &v4l2-plane; <structfield>m</structfield> union
<structfield>mem_offset</structfield> field for the multi-planar API.</para>
</listitem>
</varlistentry>
</variablelist>

3
Documentation/DocBook/v4l/func-munmap.xml
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@ -37,7 +37,8 @@
<para>Length of the mapped buffer. This must be the same
value as given to <function>mmap()</function> and returned by the
driver in the &v4l2-buffer; <structfield>length</structfield>
field.</para>
field for the single-planar API and in the &v4l2-plane;
<structfield>length</structfield> field for the multi-planar API.</para>
</listitem>
</varlistentry>
</variablelist>

247
Documentation/DocBook/v4l/io.xml
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@ -121,18 +121,22 @@ mapped.</para>
<para>Before applications can access the buffers they must map
them into their address space with the &func-mmap; function. The
location of the buffers in device memory can be determined with the
&VIDIOC-QUERYBUF; ioctl. The <structfield>m.offset</structfield> and
<structfield>length</structfield> returned in a &v4l2-buffer; are
passed as sixth and second parameter to the
<function>mmap()</function> function. The offset and length values
must not be modified. Remember the buffers are allocated in physical
memory, as opposed to virtual memory which can be swapped out to disk.
Applications should free the buffers as soon as possible with the
&func-munmap; function.</para>
&VIDIOC-QUERYBUF; ioctl. In the single-planar API case, the
<structfield>m.offset</structfield> and <structfield>length</structfield>
returned in a &v4l2-buffer; are passed as sixth and second parameter to the
<function>mmap()</function> function. When using the multi-planar API,
struct &v4l2-buffer; contains an array of &v4l2-plane; structures, each
containing its own <structfield>m.offset</structfield> and
<structfield>length</structfield>. When using the multi-planar API, every
plane of every buffer has to be mapped separately, so the number of
calls to &func-mmap; should be equal to number of buffers times number of
planes in each buffer. The offset and length values must not be modified.
Remember, the buffers are allocated in physical memory, as opposed to virtual
memory, which can be swapped out to disk. Applications should free the buffers
as soon as possible with the &func-munmap; function.</para>
<example>
<title>Mapping buffers</title>
<title>Mapping buffers in the single-planar API</title>
<programlisting>
&v4l2-requestbuffers; reqbuf;
struct {
@ -201,6 +205,88 @@ for (i = 0; i &lt; reqbuf.count; i++)
</programlisting>
</example>
<example>
<title>Mapping buffers in the multi-planar API</title>
<programlisting>
&v4l2-requestbuffers; reqbuf;
/* Our current format uses 3 planes per buffer */
#define FMT_NUM_PLANES = 3;
struct {
void *start[FMT_NUM_PLANES];
size_t length[FMT_NUM_PLANES];
} *buffers;
unsigned int i, j;
memset(&amp;reqbuf, 0, sizeof(reqbuf));
reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
reqbuf.memory = V4L2_MEMORY_MMAP;
reqbuf.count = 20;
if (ioctl(fd, &VIDIOC-REQBUFS;, &amp;reqbuf) &lt; 0) {
if (errno == EINVAL)
printf("Video capturing or mmap-streaming is not supported\n");
else
perror("VIDIOC_REQBUFS");
exit(EXIT_FAILURE);
}
/* We want at least five buffers. */
if (reqbuf.count &lt; 5) {
/* You may need to free the buffers here. */
printf("Not enough buffer memory\n");
exit(EXIT_FAILURE);
}
buffers = calloc(reqbuf.count, sizeof(*buffers));
assert(buffers != NULL);
for (i = 0; i &lt; reqbuf.count; i++) {
&v4l2-buffer; buffer;
&v4l2-plane; planes[FMT_NUM_PLANES];
memset(&amp;buffer, 0, sizeof(buffer));
buffer.type = reqbuf.type;
buffer.memory = V4L2_MEMORY_MMAP;
buffer.index = i;
/* length in struct v4l2_buffer in multi-planar API stores the size
* of planes array. */
buffer.length = FMT_NUM_PLANES;
buffer.m.planes = planes;
if (ioctl(fd, &VIDIOC-QUERYBUF;, &amp;buffer) &lt; 0) {
perror("VIDIOC_QUERYBUF");
exit(EXIT_FAILURE);
}
/* Every plane has to be mapped separately */
for (j = 0; j &lt; FMT_NUM_PLANES; j++) {
buffers[i].length[j] = buffer.m.planes[j].length; /* remember for munmap() */
buffers[i].start[j] = mmap(NULL, buffer.m.planes[j].length,
PROT_READ | PROT_WRITE, /* recommended */
MAP_SHARED, /* recommended */
fd, buffer.m.planes[j].m.offset);
if (MAP_FAILED == buffers[i].start[j]) {
/* If you do not exit here you should unmap() and free()
the buffers and planes mapped so far. */
perror("mmap");
exit(EXIT_FAILURE);
}
}
}
/* Cleanup. */
for (i = 0; i &lt; reqbuf.count; i++)
for (j = 0; j &lt; FMT_NUM_PLANES; j++)
munmap(buffers[i].start[j], buffers[i].length[j]);
</programlisting>
</example>
<para>Conceptually streaming drivers maintain two buffer queues, an incoming
and an outgoing queue. They separate the synchronous capture or output
operation locked to a video clock from the application which is
@ -286,13 +372,13 @@ pointer method (not only memory mapping) is supported must be
determined by calling the &VIDIOC-REQBUFS; ioctl.</para>
<para>This I/O method combines advantages of the read/write and
memory mapping methods. Buffers are allocated by the application
memory mapping methods. Buffers (planes) are allocated by the application
itself, and can reside for example in virtual or shared memory. Only
pointers to data are exchanged, these pointers and meta-information
are passed in &v4l2-buffer;. The driver must be switched
into user pointer I/O mode by calling the &VIDIOC-REQBUFS; with the
desired buffer type. No buffers are allocated beforehands,
consequently they are not indexed and cannot be queried like mapped
are passed in &v4l2-buffer; (or in &v4l2-plane; in the multi-planar API case).
The driver must be switched into user pointer I/O mode by calling the
&VIDIOC-REQBUFS; with the desired buffer type. No buffers (planes) are allocated
beforehand, consequently they are not indexed and cannot be queried like mapped
buffers with the <constant>VIDIOC_QUERYBUF</constant> ioctl.</para>
<example>
@ -316,7 +402,7 @@ if (ioctl (fd, &VIDIOC-REQBUFS;, &amp;reqbuf) == -1) {
</programlisting>
</example>
<para>Buffer addresses and sizes are passed on the fly with the
<para>Buffer (plane) addresses and sizes are passed on the fly with the
&VIDIOC-QBUF; ioctl. Although buffers are commonly cycled,
applications can pass different addresses and sizes at each
<constant>VIDIOC_QBUF</constant> call. If required by the hardware the
@ -396,11 +482,18 @@ rest should be evident.</para>
<title>Buffers</title>
<para>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 <structname>v4l2_buffer</structname>, argument to
the &VIDIOC-QUERYBUF;, &VIDIOC-QBUF; and &VIDIOC-DQBUF; ioctl.</para>
driver using one of the Streaming I/O methods. In the multi-planar API, the
data is held in planes, while the buffer structure acts as a container
for the planes. Only pointers to buffers (planes) are exchanged, the data
itself is not copied. These pointers, together with meta-information like
timestamps or field parity, are stored in a struct
<structname>v4l2_buffer</structname>, argument to
the &VIDIOC-QUERYBUF;, &VIDIOC-QBUF; and &VIDIOC-DQBUF; ioctl.
In the multi-planar API, some plane-specific members of struct
<structname>v4l2_buffer</structname>, such as pointers and sizes for each
plane, are stored in struct <structname>v4l2_plane</structname> instead.
In that case, struct <structname>v4l2_buffer</structname> contains an array of
plane structures.</para>
<para>Nominally timestamps refer to the first data byte transmitted.
In practice however the wide range of hardware covered by the V4L2 API
@ -551,26 +644,40 @@ in accordance with the selected I/O method.</entry>
<entry></entry>
<entry>__u32</entry>
<entry><structfield>offset</structfield></entry>
<entry>When <structfield>memory</structfield> is
<constant>V4L2_MEMORY_MMAP</constant> 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 &func-mmap; function
not useful for applications. See <xref linkend="mmap" /> for details.</entry>
<entry>For the single-planar API and when
<structfield>memory</structfield> is <constant>V4L2_MEMORY_MMAP</constant> 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 &func-mmap;
function not useful for applications. See <xref linkend="mmap" /> for details
</entry>
</row>
<row>
<entry></entry>
<entry>unsigned long</entry>
<entry><structfield>userptr</structfield></entry>
<entry>When <structfield>memory</structfield> is
<constant>V4L2_MEMORY_USERPTR</constant> this is a pointer to the
buffer (casted to unsigned long type) in virtual memory, set by the
application. See <xref linkend="userp" /> for details.</entry>
<entry>For the single-planar API and when
<structfield>memory</structfield> is <constant>V4L2_MEMORY_USERPTR</constant>
this is a pointer to the buffer (casted to unsigned long type) in virtual
memory, set by the application. See <xref linkend="userp" /> for details.
</entry>
</row>
<row>
<entry></entry>
<entry>struct v4l2_plane</entry>
<entry><structfield>*planes</structfield></entry>
<entry>When using the multi-planar API, contains a userspace pointer
to an array of &v4l2-plane;. The size of the array should be put
in the <structfield>length</structfield> field of this
<structname>v4l2_buffer</structname> structure.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>length</structfield></entry>
<entry></entry>
<entry>Size of the buffer (not the payload) in bytes.</entry>
<entry>Size of the buffer (not the payload) in bytes for the
single-planar API. For the multi-planar API should contain the
number of elements in the <structfield>planes</structfield> array.
</entry>
</row>
<row>
<entry>__u32</entry>
@ -596,6 +703,66 @@ should set this to 0.</entry>
</tgroup>
</table>
<table frame="none" pgwide="1" id="v4l2-plane">
<title>struct <structname>v4l2_plane</structname></title>
<tgroup cols="4">
&cs-ustr;
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>bytesused</structfield></entry>
<entry></entry>
<entry>The number of bytes occupied by data in the plane
(its payload).</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>length</structfield></entry>
<entry></entry>
<entry>Size in bytes of the plane (not its payload).</entry>
</row>
<row>
<entry>union</entry>
<entry><structfield>m</structfield></entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry></entry>
<entry>__u32</entry>
<entry><structfield>mem_offset</structfield></entry>
<entry>When the memory type in the containing &v4l2-buffer; is
<constant>V4L2_MEMORY_MMAP</constant>, this is the value that
should be passed to &func-mmap;, similar to the
<structfield>offset</structfield> field in &v4l2-buffer;.</entry>
</row>
<row>
<entry></entry>
<entry>__unsigned long</entry>
<entry><structfield>userptr</structfield></entry>
<entry>When the memory type in the containing &v4l2-buffer; is
<constant>V4L2_MEMORY_USERPTR</constant>, this is a userspace
pointer to the memory allocated for this plane by an application.
</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>data_offset</structfield></entry>
<entry></entry>
<entry>Offset in bytes to video data in the plane, if applicable.
</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>reserved[11]</structfield></entry>
<entry></entry>
<entry>Reserved for future use. Should be zeroed by an
application.</entry>
</row>
</tbody>
</tgroup>
</table>
<table frame="none" pgwide="1" id="v4l2-buf-type">
<title>enum v4l2_buf_type</title>
<tgroup cols="3">
@ -604,13 +771,27 @@ should set this to 0.</entry>
<row>
<entry><constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant></entry>
<entry>1</entry>
<entry>Buffer of a video capture stream, see <xref
<entry>Buffer of a single-planar video capture stream, see <xref
linkend="capture" />.</entry>
</row>
<row>
<entry><constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>
</entry>
<entry>9</entry>
<entry>Buffer of a multi-planar video capture stream, see <xref
linkend="capture" />.</entry>
</row>
<row>
<entry><constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant></entry>
<entry>2</entry>
<entry>Buffer of a video output stream, see <xref
<entry>Buffer of a single-planar video output stream, see <xref
linkend="output" />.</entry>
</row>
<row>
<entry><constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>
</entry>
<entry>10</entry>
<entry>Buffer of a multi-planar video output stream, see <xref
linkend="output" />.</entry>
</row>
<row>

116
Documentation/DocBook/v4l/pixfmt.xml
View File

@ -2,12 +2,16 @@
<para>The V4L2 API was primarily designed for devices exchanging
image data with applications. The
<structname>v4l2_pix_format</structname> structure defines the format
and layout of an image in memory. Image formats are negotiated with
the &VIDIOC-S-FMT; ioctl. (The explanations here focus on video
<structname>v4l2_pix_format</structname> and <structname>v4l2_pix_format_mplane
</structname> structures define the format and layout of an image in memory.
The former is used with the single-planar API, while the latter is used with the
multi-planar version (see <xref linkend="planar-apis"/>). Image formats are
negotiated with the &VIDIOC-S-FMT; ioctl. (The explanations here focus on video
capturing and output, for overlay frame buffer formats see also
&VIDIOC-G-FBUF;.)</para>
<section>
<title>Single-planar format structure</title>
<table pgwide="1" frame="none" id="v4l2-pix-format">
<title>struct <structname>v4l2_pix_format</structname></title>
<tgroup cols="3">
@ -106,6 +110,98 @@ set this field to zero.</entry>
</tbody>
</tgroup>
</table>
</section>
<section>
<title>Multi-planar format structures</title>
<para>The <structname>v4l2_plane_pix_format</structname> structures define
size and layout for each of the planes in a multi-planar format.
The <structname>v4l2_pix_format_mplane</structname> structure contains
information common to all planes (such as image width and height) and
an array of <structname>v4l2_plane_pix_format</structname> structures,
describing all planes of that format.</para>
<table pgwide="1" frame="none" id="v4l2-plane-pix-format">
<title>struct <structname>vl42_plane_pix_format</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>sizeimage</structfield></entry>
<entry>Maximum size in bytes required for image data in this plane.
</entry>
</row>
<row>
<entry>__u16</entry>
<entry><structfield>bytesperline</structfield></entry>
<entry>Distance in bytes between the leftmost pixels in two adjacent
lines.</entry>
</row>
<row>
<entry>__u16</entry>
<entry><structfield>reserved[7]</structfield></entry>
<entry>Reserved for future extensions. Should be zeroed by the
application.</entry>
</row>
</tbody>
</tgroup>
</table>
<table pgwide="1" frame="none" id="v4l2-pix-format-mplane">
<title>struct <structname>v4l2_pix_format_mplane</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>width</structfield></entry>
<entry>Image width in pixels.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>height</structfield></entry>
<entry>Image height in pixels.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>pixelformat</structfield></entry>
<entry>The pixel format. Both single- and multi-planar four character
codes can be used.</entry>
</row>
<row>
<entry>&v4l2-field;</entry>
<entry><structfield>field</structfield></entry>
<entry>See &v4l2-pix-format;.</entry>
</row>
<row>
<entry>&v4l2-colorspace;</entry>
<entry><structfield>colorspace</structfield></entry>
<entry>See &v4l2-pix-format;.</entry>
</row>
<row>
<entry>&v4l2-plane-pix-format;</entry>
<entry><structfield>plane_fmt[VIDEO_MAX_PLANES]</structfield></entry>
<entry>An array of structures describing format of each plane this
pixel format consists of. The number of valid entries in this array
has to be put in the <structfield>num_planes</structfield>
field.</entry>
</row>
<row>
<entry>__u8</entry>
<entry><structfield>num_planes</structfield></entry>
<entry>Number of planes (i.e. separate memory buffers) for this format
and the number of valid entries in the
<structfield>plane_fmt</structfield> array.</entry>
</row>
<row>
<entry>__u8</entry>
<entry><structfield>reserved[11]</structfield></entry>
<entry>Reserved for future extensions. Should be zeroed by the
application.</entry>
</row>
</tbody>
</tgroup>
</table>
</section>
<section>
<title>Standard Image Formats</title>
@ -142,11 +238,19 @@ leftmost pixel of the second row from the top, and so on. The last row
has just as many pad bytes after it as the other rows.</para>
<para>In V4L2 each format has an identifier which looks like
<constant>PIX_FMT_XXX</constant>, defined in the <filename>videodev2.h</filename>
header file. These identifiers
represent <link linkend="v4l2-fourcc">four character codes</link>
<constant>PIX_FMT_XXX</constant>, defined in the <link
linkend="videodev">videodev.h</link> header file. These identifiers
represent <link linkend="v4l2-fourcc">four character (FourCC) codes</link>
which are also listed below, however they are not the same as those
used in the Windows world.</para>
<para>For some formats, data is stored in separate, discontiguous
memory buffers. Those formats are identified by a separate set of FourCC codes
and are referred to as "multi-planar formats". For example, a YUV422 frame is
normally stored in one memory buffer, but it can also be placed in two or three
separate buffers, with Y component in one buffer and CbCr components in another
in the 2-planar version or with each component in its own buffer in the
3-planar case. Those sub-buffers are referred to as "planes".</para>
</section>
<section id="colorspaces">

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@ -0,0 +1,81 @@
<section id="planar-apis">
<title>Single- and multi-planar APIs</title>
<para>Some devices require data for each input or output video frame
to be placed in discontiguous memory buffers. In such cases one
video frame has to be addressed using more than one memory address, i.e. one
pointer per "plane". A plane is a sub-buffer of current frame. For examples
of such formats see <xref linkend="pixfmt" />.</para>
<para>Initially, V4L2 API did not support multi-planar buffers and a set of
extensions has been introduced to handle them. Those extensions constitute
what is being referred to as the "multi-planar API".</para>
<para>Some of the V4L2 API calls and structures are interpreted differently,
depending on whether single- or multi-planar API is being used. An application
can choose whether to use one or the other by passing a corresponding buffer
type to its ioctl calls. Multi-planar versions of buffer types are suffixed with
an `_MPLANE' string. For a list of available multi-planar buffer types
see &v4l2-buf-type;.
</para>
<section>
<title>Multi-planar formats</title>
<para>Multi-planar API introduces new multi-planar formats. Those formats
use a separate set of FourCC codes. It is important to distinguish between
the multi-planar API and a multi-planar format. Multi-planar API calls can
handle all single-planar formats as well, while the single-planar API cannot
handle multi-planar formats. Applications do not have to switch between APIs
when handling both single- and multi-planar devices and should use the
multi-planar API version for both single- and multi-planar formats.
Drivers that do not support multi-planar API can still be handled with it,
utilizing a compatibility layer built into standard V4L2 ioctl handling.
</para>
</section>
<section>
<title>Single and multi-planar API compatibility layer</title>
<para>In most cases<footnote><para>The compatibility layer does not cover
drivers that do not use video_ioctl2() call.</para></footnote>, applications
can use the multi-planar API with older drivers that support
only its single-planar version and vice versa. Appropriate conversion is
done seamlessly for both applications and drivers in the V4L2 core. The
general rule of thumb is: as long as an application uses formats that
a driver supports, it can use either API (although use of multi-planar
formats is only possible with the multi-planar API). The list of formats
supported by a driver can be obtained using the &VIDIOC-ENUM-FMT; call.
It is possible, but discouraged, for a driver or an application to support
and use both versions of the API.</para>
</section>
<section>
<title>Calls that distinguish between single and multi-planar APIs</title>
<variablelist>
<varlistentry>
<term>&VIDIOC-QUERYCAP;</term>
<listitem>Two additional multi-planar capabilities are added. They can
be set together with non-multi-planar ones for devices that handle
both single- and multi-planar formats.</listitem>
</varlistentry>
<varlistentry>
<term>&VIDIOC-G-FMT;, &VIDIOC-S-FMT;, &VIDIOC-TRY-FMT;</term>
<listitem>New structures for describing multi-planar formats are added:
&v4l2-pix-format-mplane; and &v4l2-plane-pix-format;. Drivers may
define new multi-planar formats, which have distinct FourCC codes from
the existing single-planar ones.
</listitem>
</varlistentry>
<varlistentry>
<term>&VIDIOC-QBUF;, &VIDIOC-DQBUF;, &VIDIOC-QUERYBUF;</term>
<listitem>A new &v4l2-plane; structure for describing planes is added.
Arrays of this structure are passed in the new
<structfield>m.planes</structfield> field of &v4l2-buffer;.
</listitem>
</varlistentry>
<varlistentry>
<term>&VIDIOC-REQBUFS;</term>
<listitem>Will allocate multi-planar buffers as requested.</listitem>
</varlistentry>
</variablelist>
</section>
</section>

21
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View File

@ -85,6 +85,17 @@ Remote Controller chapter.</contrib>
</address>
</affiliation>
</author>
<author>
<firstname>Pawel</firstname>
<surname>Osciak</surname>
<contrib>Designed and documented the multi-planar API.</contrib>
<affiliation>
<address>
<email>pawel AT osciak.com</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
@ -102,7 +113,8 @@ Remote Controller chapter.</contrib>
<year>2010</year>
<year>2011</year>
<holder>Bill Dirks, Michael H. Schimek, Hans Verkuil, Martin
Rubli, Andy Walls, Muralidharan Karicheri, Mauro Carvalho Chehab</holder>
Rubli, Andy Walls, Muralidharan Karicheri, Mauro Carvalho Chehab,
Pawel Osciak</holder>
</copyright>
<legalnotice>
<para>Except when explicitly stated as GPL, programming examples within
@ -115,6 +127,13 @@ structs, ioctls) must be noted in more detail in the history chapter
(compat.xml), along with the possible impact on existing drivers and
applications. -->
<revision>
<revnumber>2.6.38</revnumber>
<authorinitials>po</authorinitials>
<revremark>Added the <link linkend="planar-apis">multi-planar API</link>.
</revremark>
</revision>
<revision>
<revnumber>2.6.37</revnumber>
<date>2010-08-06</date>

2
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View File

@ -76,7 +76,9 @@ pixelformat</structfield> field.</entry>
<entry>Type of the data stream, set by the application.
Only these types are valid here:
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>, and custom (driver
defined) types with code <constant>V4L2_BUF_TYPE_PRIVATE</constant>
and higher.</entry>

15
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View File

@ -60,11 +60,13 @@ application.</para>
<structfield>type</structfield> field of a struct
<structname>v4l2_format</structname> to the respective buffer (stream)
type. For example video capture devices use
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>. When the application
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> or
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>. When the application
calls the <constant>VIDIOC_G_FMT</constant> ioctl with a pointer to
this structure the driver fills the respective member of the
<structfield>fmt</structfield> union. In case of video capture devices
that is the &v4l2-pix-format; <structfield>pix</structfield> member.
that is either the &v4l2-pix-format; <structfield>pix</structfield> or
the &v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member.
When the requested buffer type is not supported drivers return an
&EINVAL;.</para>
@ -131,6 +133,15 @@ this ioctl.</para>
<entry>Definition of an image format, see <xref
linkend="pixfmt" />, used by video capture and output
devices.</entry>
</row>
<row>
<entry></entry>
<entry>&v4l2-pix-format-mplane;</entry>
<entry><structfield>pix_mp</structfield></entry>
<entry>Definition of an image format, see <xref
linkend="pixfmt" />, used by video capture and output
devices that support the <link linkend="planar-apis">multi-planar
version of the API</link>.</entry>
</row>
<row>
<entry></entry>

24
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View File

@ -64,7 +64,8 @@ zero to the number of buffers allocated with &VIDIOC-REQBUFS;
contents of the struct <structname>v4l2_buffer</structname> returned
by a &VIDIOC-QUERYBUF; ioctl will do as well. When the buffer is
intended for output (<structfield>type</structfield> is
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> or
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>, or
<constant>V4L2_BUF_TYPE_VBI_OUTPUT</constant>) applications must also
initialize the <structfield>bytesused</structfield>,
<structfield>field</structfield> and
@ -75,7 +76,11 @@ supports capturing from specific video inputs and you want to specify a video
input, then <structfield>flags</structfield> should be set to
<constant>V4L2_BUF_FLAG_INPUT</constant> and the field
<structfield>input</structfield> must be initialized to the desired input.
The <structfield>reserved</structfield> field must be set to 0.
The <structfield>reserved</structfield> field must be set to 0. When using
the <link linkend="planar-apis">multi-planar API</link>, the
<structfield>m.planes</structfield> field must contain a userspace pointer
to a filled-in array of &v4l2-plane; and the <structfield>length</structfield>
field must be set to the number of elements in that array.
</para>
<para>To enqueue a <link linkend="mmap">memory mapped</link>
@ -93,10 +98,13 @@ structure the driver sets the
buffer applications set the <structfield>memory</structfield>
field to <constant>V4L2_MEMORY_USERPTR</constant>, the
<structfield>m.userptr</structfield> field to the address of the
buffer and <structfield>length</structfield> to its size.
When <constant>VIDIOC_QBUF</constant> is called with a pointer to this
structure the driver sets the <constant>V4L2_BUF_FLAG_QUEUED</constant>
flag and clears the <constant>V4L2_BUF_FLAG_MAPPED</constant> and
buffer and <structfield>length</structfield> to its size. When the multi-planar
API is used, <structfield>m.userptr</structfield> and
<structfield>length</structfield> members of the passed array of &v4l2-plane;
have to be used instead. When <constant>VIDIOC_QBUF</constant> is called with
a pointer to this structure the driver sets the
<constant>V4L2_BUF_FLAG_QUEUED</constant> flag and clears the
<constant>V4L2_BUF_FLAG_MAPPED</constant> and
<constant>V4L2_BUF_FLAG_DONE</constant> flags in the
<structfield>flags</structfield> field, or it returns an error code.
This ioctl locks the memory pages of the buffer in physical memory,
@ -115,7 +123,9 @@ remaining fields or returns an error code. The driver may also set
<constant>V4L2_BUF_FLAG_ERROR</constant> in the <structfield>flags</structfield>
field. It indicates a non-critical (recoverable) streaming error. In such case
the application may continue as normal, but should be aware that data in the
dequeued buffer might be corrupted.</para>
dequeued buffer might be corrupted. When using the multi-planar API, the
planes array does not have to be passed; the <structfield>m.planes</structfield>
member must be set to NULL in that case.</para>
<para>By default <constant>VIDIOC_DQBUF</constant> blocks when no
buffer is in the outgoing queue. When the

14
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View File

@ -61,6 +61,10 @@ buffer at any time after buffers have been allocated with the
to the number of buffers allocated with &VIDIOC-REQBUFS;
(&v4l2-requestbuffers; <structfield>count</structfield>) minus one.
The <structfield>reserved</structfield> field should to set to 0.
When using the <link linkend="planar-apis">multi-planar API</link>, the
<structfield>m.planes</structfield> field must contain a userspace pointer to an
array of &v4l2-plane; and the <structfield>length</structfield> field has
to be set to the number of elements in that array.
After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to
this structure drivers return an error code or fill the rest of
the structure.</para>
@ -70,11 +74,13 @@ the structure.</para>
<constant>V4L2_BUF_FLAG_QUEUED</constant> and
<constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The
<structfield>memory</structfield> field will be set to the current
I/O method, the <structfield>m.offset</structfield>
I/O method. For the single-planar API, the <structfield>m.offset</structfield>
contains the offset of the buffer from the start of the device memory,
the <structfield>length</structfield> field its size. The driver may
or may not set the remaining fields and flags, they are meaningless in
this context.</para>
the <structfield>length</structfield> field its size. For the multi-planar API,
fields <structfield>m.mem_offset</structfield> and
<structfield>length</structfield> in the <structfield>m.planes</structfield>
array elements will be used instead. The driver may or may not set the remaining
fields and flags, they are meaningless in this context.</para>
<para>The <structname>v4l2_buffer</structname> structure is
specified in <xref linkend="buffer" />.</para>

24
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View File

@ -142,14 +142,30 @@ this array to zero.</entry>
<row>
<entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
<entry>0x00000001</entry>
<entry>The device supports the <link
linkend="capture">Video Capture</link> interface.</entry>
<entry>The device supports single-planar formats through the <link
linkend="capture">Video Capture</link> interface. An application can use either
<link linkend="planar-apis">the single or the multi-planar API</link>.</entry>
</row>
<row>
<entry><constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant></entry>
<entry>0x00001000</entry>
<entry>The device supports multi-planar formats through the <link
linkend="capture">Video Capture</link> interface. An application has to use the
<link linkend="planar-apis">multi-planar API</link>.</entry>
</row>
<row>
<entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
<entry>0x00000002</entry>
<entry>The device supports the <link
linkend="output">Video Output</link> interface.</entry>
<entry>The device supports single-planar formats through the <link
linkend="output">Video Output</link> interface. An application can use either
<link linkend="planar-apis">the single or the multi-planar API</link>.</entry>
</row>
<row>
<entry><constant>V4L2_CAP_VIDEO_OUTPUT_MPLANE</constant></entry>
<entry>0x00002000</entry>
<entry>The device supports multi-planar formats through the <link
linkend="output">Video Output</link> interface. An application has to use the
<link linkend="planar-apis">multi-planar API</link>.</entry>
</row>
<row>
<entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>