driver. Anyway, drivers may not support single field capturing and
return both count values non-zero.
- Both ``count`` values set to zero, or line numbers outside the
- bounds depicted in :ref:`vbi-525` and :ref:`vbi-625`, or a
- field image covering lines of two fields, are invalid and shall
- not be returned by the driver.
+ Both ``count`` values set to zero, or line numbers are outside the
+ bounds depicted\ [#f4]_, or a field image covering lines of two
+ fields, are invalid and shall not be returned by the driver.
To initialize the ``start`` and ``count`` fields, applications
must first determine the current video standard selection. The
Most VBI services transmit on both fields, but some have different
semantics depending on the field number. These cannot be reliable
decoded or encoded when ``V4L2_VBI_UNSYNC`` is set.
+
+.. [#f4]
+ The valid values ar shown at :ref:`vbi-525` and :ref:`vbi-625`.