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-rw-r--r--Documentation/DocBook/media/v4l/io.xml9
1 files changed, 7 insertions, 2 deletions
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index a086a5db7a18..e5e8325aa3d7 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -870,7 +870,8 @@ should set this to 0.</entry>
If the application sets this to 0 for an output stream, then
<structfield>bytesused</structfield> will be set to the size of the
plane (see the <structfield>length</structfield> field of this struct)
- by the driver.</entry>
+ by the driver. Note that the actual image data starts at
+ <structfield>data_offset</structfield> which may not be 0.</entry>
</row>
<row>
<entry>__u32</entry>
@@ -919,6 +920,10 @@ should set this to 0.</entry>
<entry>Offset in bytes to video data in the plane.
Drivers must set this field when <structfield>type</structfield>
refers to an input stream, applications when it refers to an output stream.
+ Note that data_offset is included in <structfield>bytesused</structfield>.
+ So the size of the image in the plane is
+ <structfield>bytesused</structfield>-<structfield>data_offset</structfield> at
+ offset <structfield>data_offset</structfield> from the start of the plane.
</entry>
</row>
<row>
@@ -1066,7 +1071,7 @@ state, in the application domain so to say.</entry>
<entry>Drivers set or clear this flag when calling the
<constant>VIDIOC_DQBUF</constant> ioctl. It may be set by video
capture devices when the buffer contains a compressed image which is a
-key frame (or field), &ie; can be decompressed on its own. Also know as
+key frame (or field), &ie; can be decompressed on its own. Also known as
an I-frame. Applications can set this bit when <structfield>type</structfield>
refers to an output stream.</entry>
</row>