lavfi/overlay: implement shortest option

Force termination when the overlay stream ends. Simplify scripting logic,
for example when an infinite source is used to generate a background for
a composite video.

1 files changed, 16 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 75d17594af..6b7ee89ac3 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -3881,6 +3881,10 @@ same as @var{overlay_w} and @var{overlay_h}
 @item rgb
 If set to 1, force the filter to accept inputs in the RGB
 color space. Default value is 0.
+
+@item shortest
+If set to 1, force the output to terminate when the shortest input
+terminates. Default value is 0.
 @end table
 
 Be aware that frames are taken from each input video in timestamp
@@ -3941,6 +3945,18 @@ ffplay input.avi -vf 'split[b], pad=iw*2[src], [b]deshake, [src]overlay=w'
 @end example
 
 @item
+Compose output by putting two input videos side to side:
+@example
+ffmpeg -i left.avi -i right.avi -filter_complex "
+nullsrc=size=200x100 [background];
+[0:v] setpts=PTS-STARTPTS, scale=100x100 [left];
+[1:v] setpts=PTS-STARTPTS, scale=100x100 [right];
+[background][left]       overlay=shortest=1       [background+left];
+[background+left][right] overlay=shortest=1:x=100 [left+right]
+"
+@end example
+
+@item
 Chain several overlays in cascade:
 @example
 nullsrc=s=200x200 [bg];