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-rw-r--r--Documentation/DocBook/media/v4l/vidioc-querystd.xml10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/DocBook/media/v4l/vidioc-querystd.xml b/Documentation/DocBook/media/v4l/vidioc-querystd.xml
index 222348542182..3ceae35fab03 100644
--- a/Documentation/DocBook/media/v4l/vidioc-querystd.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-querystd.xml
@@ -59,6 +59,16 @@ then the driver will return V4L2_STD_UNKNOWN. When detection is not
possible or fails, the set must contain all standards supported by the
current video input or output.</para>
+<para>Please note that drivers shall <emphasis>not</emphasis> switch the video standard
+automatically if a new video standard is detected. Instead, drivers should send the
+<constant>V4L2_EVENT_SOURCE_CHANGE</constant> event (if they support this) and expect
+that userspace will take action by calling <constant>VIDIOC_QUERYSTD</constant>.
+The reason is that a new video standard can mean different buffer sizes as well, and you
+cannot change buffer sizes on the fly. In general, applications that receive the
+Source Change event will have to call <constant>VIDIOC_QUERYSTD</constant>,
+and if the detected video standard is valid they will have to stop streaming, set the new
+standard, allocate new buffers and start streaming again.</para>
+
</refsect1>
<refsect1>