[FFmpeg-cvslog] doc/indevs: Add example using cropping to capture part of a plane

[Mark Thompson]

ffmpeg | branch: master | Mark Thompson <sw at jkqxz.net> | Sat Mar 23 16:18:49 2019 +0000| [963c4f85fe547ef51fafb66d7eceb3f5637d3843] | committer: Mark Thompson

doc/indevs: Add example using cropping to capture part of a plane

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=963c4f85fe547ef51fafb66d7eceb3f5637d3843
---

 doc/indevs.texi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 1d5ed65773..89ba4fb406 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -910,6 +910,14 @@ Capture from CRTC ID 42 at 60fps, map the result to VAAPI, convert to NV12 and e
 ffmpeg -crtc_id 42 -framerate 60 -f kmsgrab -i - -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12' -c:v h264_vaapi output.mp4
 @end example
 
+ at item
+To capture only part of a plane the output can be cropped - this can be used to capture
+a single window, as long as it has a known absolute position and size.  For example, to
+capture and encode the middle quarter of a 1920x1080 plane:
+ at example
+ffmpeg -f kmsgrab -i - -vf 'hwmap=derive_device=vaapi,crop=960:540:480:270,scale_vaapi=960:540:nv12' -c:v h264_vaapi output.mp4
+ at end example
+
 @end itemize
 
 @section lavfi