lavd: implement NewTek NDI input/output device support

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

doc/outdevs.texi

@@ -182,6 +182,51 @@ ffmpeg -i test.avi -f decklink -pix_fmt uyvy422 -s 720x486 -r 24000/1001 'DeckLi
 
 @end itemize
 
+@section libndi_newtek
+
+The libndi_newtek output device provides playback capabilities for using NDI (Network
+Device Interface, standard created by NewTek).
+
+Output filename is a NDI name.
+
+To enable this output device, you need the NDI SDK and you
+need to configure with the appropriate @code{--extra-cflags}
+and @code{--extra-ldflags}.
+
+NDI uses uyvy422 pixel format natively, but also supports bgra, bgr0, rgba and
+rgb0.
+
+@subsection Options
+
+@table @option
+
+@item reference_level
+The audio reference level in dB. This specifies how many dB above the
+reference level (+4dBU) is the full range of 16 bit audio.
+Defaults to @option{0}.
+
+@item clock_video
+These specify whether video "clock" themselves.
+Defaults to @option{false}.
+
+@item clock_audio
+These specify whether audio "clock" themselves.
+Defaults to @option{false}.
+
+@end table
+
+@subsection Examples
+
+@itemize
+
+@item
+Play video clip:
+@example
+ffmpeg -i "udp://@@239.1.1.1:10480?fifo_size=1000000&overrun_nonfatal=1" -vf "scale=720:576,fps=fps=25,setdar=dar=16/9,format=pix_fmts=uyvy422" -f libndi_newtek NEW_NDI1
+@end example
+
+@end itemize
+
 @section fbdev
 
 Linux framebuffer output device.