Write about video signal numbers.

diff --git a/video.rst b/video.rst
index cdef8f194674cc3343258fe2cd95ca5e73eed7b7..4e7c41ec1c45ee949154e4890819130916c66de8 100644 (file)
--- a/video.rst
+++ b/video.rst
@@ -61,6 +61,15 @@ moving the new file atomically into place, you could end up corrupting the file
 Nageru is playing from, causing it to automatically rewind before the end of
 the segment.
 
+Videos are assigned an arbitrary signal number when loaded. Whenever you need
+to refer to this signal number (say, to get its width or height for display),
+you should use *video:get_signal_num()*. Like any other signal, videos have
+a width and height, an interlaced flag (currently always false), a frame rate
+(which can vary during playback) and has_signal/is_connected member functions.
+The former is always true, but the former will be false if the video isn't
+currently playing for whatever reason (e.g., the file is corrupted, or a network
+stream is broken and hasn't reconnected yet).
+
 
 Controlling video playback
 --------------------------