nut: Support experimental NUT 4 features

Add the low overhead pipe mode and the extended broadcast mode.
Export the options as 'syncponts' since it impacts only that.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

doc/muxers.texi

@@ -444,6 +444,23 @@ Alternatively you can write the command as:
 avconv -benchmark -i INPUT -f null -
 @end example
 
+@section nut
+
+@table @option
+@item -syncpoints @var{flags}
+Change the syncpoint usage in nut:
+@table @option
+@item @var{default} use the normal low-overhead seeking aids.
+@item @var{none} do not use the syncpoints at all, reducing the overhead but making the stream non-seekable;
+@item @var{timestamped} extend the syncpoint with a wallclock field.
+@end table
+The @var{none} and @var{timestamped} flags are experimental.
+@end table
+
+@example
+avconv -i INPUT -f_strict experimental -syncpoints none - | processor
+@end example
+
 @section ogg
 
 Ogg container muxer.

doc/nut.texi

@@ -17,6 +17,27 @@ subtitle and user-defined streams in a simple, yet efficient, way.
 It was created by a group of FFmpeg and MPlayer developers in 2003
 and was finalized in 2008.
 
+@chapter Modes
+NUT has some variants signaled by using the flags field in its main header.
+
+@multitable @columnfractions .4 .4
+@item BROADCAST   @tab Extend the syncpoint to report the sender wallclock
+@item PIPE        @tab Omit completely the syncpoint
+@end multitable
+
+@section BROADCAST
+
+The BROADCAST variant provides a secondary time reference to facilitate
+detecting endpoint latency and network delays.
+It assumes all the endpoint clocks are syncronized.
+To be used in real-time scenarios.
+
+@section PIPE
+
+The PIPE variant assumes NUT is used as non-seekable intermediate container,
+by not using syncpoint removes unneeded overhead and reduces the overall
+memory usage.
+
 @chapter Container-specific codec tags
 
 @section Generic raw YUVA formats