diff options
Diffstat (limited to 'Documentation/DocBook/media/v4l/common.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/common.xml | 30 |
1 files changed, 14 insertions, 16 deletions
diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml index b91d25313b6..73c6847436c 100644 --- a/Documentation/DocBook/media/v4l/common.xml +++ b/Documentation/DocBook/media/v4l/common.xml @@ -564,7 +564,7 @@ automatically.</para> <para>To query and select the standard used by the current video input or output applications call the &VIDIOC-G-STD; and &VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis> -standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote> +standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote> <para>An alternative to the current scheme is to use pointers to indices as arguments of <constant>VIDIOC_G_STD</constant> and <constant>VIDIOC_S_STD</constant>, the &v4l2-input; and @@ -588,30 +588,28 @@ switch to a standard by &v4l2-std-id;.</para> </footnote> Drivers must implement all video standard ioctls when the device has one or more video inputs or outputs.</para> - <para>Special rules apply to USB cameras where the notion of video -standards makes little sense. More generally any capture device, -output devices accordingly, which is <itemizedlist> + <para>Special rules apply to devices such as USB cameras where the notion of video +standards makes little sense. More generally for any capture or output device +which is: <itemizedlist> <listitem> <para>incapable of capturing fields or frames at the nominal rate of the video standard, or</para> </listitem> <listitem> - <para>where <link linkend="buffer">timestamps</link> refer -to the instant the field or frame was received by the driver, not the -capture time, or</para> - </listitem> - <listitem> - <para>where <link linkend="buffer">sequence numbers</link> -refer to the frames received by the driver, not the captured -frames.</para> + <para>that does not support the video standard formats at all.</para> </listitem> </itemizedlist> Here the driver shall set the <structfield>std</structfield> field of &v4l2-input; and &v4l2-output; -to zero, the <constant>VIDIOC_G_STD</constant>, +to zero and the <constant>VIDIOC_G_STD</constant>, <constant>VIDIOC_S_STD</constant>, <constant>VIDIOC_QUERYSTD</constant> and <constant>VIDIOC_ENUMSTD</constant> ioctls shall return the -&EINVAL;.<footnote> +&ENOTTY;.<footnote> + <para>See <xref linkend="buffer" /> for a rationale.</para> + <para>Applications can make use of the <xref linkend="input-capabilities" /> and +<xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls +are available for the device.</para> +&ENOTTY;. <para>See <xref linkend="buffer" /> for a rationale. Probably even USB cameras follow some well known video standard. It might have been better to explicitly indicate elsewhere if a device cannot live @@ -626,9 +624,9 @@ up to normal expectations, instead of this exception.</para> &v4l2-standard; standard; if (-1 == ioctl (fd, &VIDIOC-G-STD;, &std_id)) { - /* Note when VIDIOC_ENUMSTD always returns EINVAL this + /* Note when VIDIOC_ENUMSTD always returns ENOTTY this is no video device or it falls under the USB exception, - and VIDIOC_G_STD returning EINVAL is no error. */ + and VIDIOC_G_STD returning ENOTTY is no error. */ perror ("VIDIOC_G_STD"); exit (EXIT_FAILURE); |