lavd: implement NewTek NDI input/output device support

Signed-off-by: Marton Balint <cus@passwd.hu>

doc/indevs.texi

@@ -332,6 +332,54 @@ ffmpeg -channels 16 -format_code Hi50 -f decklink -i 'UltraStudio Mini Recorder'
 
 @end itemize
 
+@section libndi_newtek
+
+The libndi_newtek input device provides capture capabilities for using NDI (Network
+Device Interface, standard created by NewTek).
+
+Input filename is a NDI source name that could be found by sending -find_sources 1
+to command line - it has no specific syntax but human-readable formatted.
+
+To enable this input device, you need the NDI SDK and you
+need to configure with the appropriate @code{--extra-cflags}
+and @code{--extra-ldflags}.
+
+@subsection Options
+
+@table @option
+
+@item find_sources
+If set to @option{true}, print a list of found/available NDI sources and exit.
+Defaults to @option{false}.
+
+@item wait_sources
+Override time to wait until the number of online sources have changed.
+Defaults to @option{0.5}.
+
+@item allow_video_fields
+When this flag is @option{false}, all video that you receive will be progressive.
+Defaults to @option{true}.
+
+@end table
+
+@subsection Examples
+
+@itemize
+
+@item
+List input devices:
+@example
+ffmpeg -f libndi_newtek -find_sources 1 -i dummy
+@end example
+
+@item
+Restream to NDI:
+@example
+ffmpeg -f libndi_newtek -i "DEV-5.INTERNAL.M1STEREO.TV (NDI_SOURCE_NAME_1)" -f libndi_newtek -y NDI_SOURCE_NAME_2
+@end example
+
+@end itemize
+
 @section dshow
 
 Windows DirectShow input device.