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-rw-r--r--Documentation/media/uapi/v4l/field-order.rst17
1 files changed, 11 insertions, 6 deletions
diff --git a/Documentation/media/uapi/v4l/field-order.rst b/Documentation/media/uapi/v4l/field-order.rst
index d640e922a974..c422bebe4314 100644
--- a/Documentation/media/uapi/v4l/field-order.rst
+++ b/Documentation/media/uapi/v4l/field-order.rst
@@ -51,6 +51,11 @@ determined by the video standard. Hence the distinction between temporal
and spatial order of fields. The diagrams below should make this
clearer.
+In V4L it is assumed that all video cameras transmit fields on the media
+bus in the same order they were captured, so if the top field was
+captured first (is the older field), the top field is also transmitted
+first on the bus.
+
All video capture and output devices must report the current field
order. Some drivers may permit the selection of a different order, to
this end applications initialize the ``field`` field of struct
@@ -101,10 +106,10 @@ enum v4l2_field
* - ``V4L2_FIELD_INTERLACED``
- 4
- Images contain both fields, interleaved line by line. The temporal
- order of the fields (whether the top or bottom field is first
- transmitted) depends on the current video standard. M/NTSC
- transmits the bottom field first, all other standards the top
- field first.
+ order of the fields (whether the top or bottom field is older)
+ depends on the current video standard. In M/NTSC the bottom
+ field is the older field. In all other standards the top field
+ is the older field.
* - ``V4L2_FIELD_SEQ_TB``
- 5
- Images contain both fields, the top field lines are stored first
@@ -135,11 +140,11 @@ enum v4l2_field
* - ``V4L2_FIELD_INTERLACED_TB``
- 8
- Images contain both fields, interleaved line by line, top field
- first. The top field is transmitted first.
+ first. The top field is the older field.
* - ``V4L2_FIELD_INTERLACED_BT``
- 9
- Images contain both fields, interleaved line by line, top field
- first. The bottom field is transmitted first.
+ first. The bottom field is the older field.