vf_scale: add force_original_aspect_ratio

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 27 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index cd590573cf..0adec4b809 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -6373,6 +6373,33 @@ Full range (0-255 in case of 8bit luma)
 "Mpeg" range (16-235 in case of 8bit luma)
 @end table
 
+@item force_original_aspect_ratio
+Enable decreasing or increasing output video width or height if necessary to
+keep the original aspect ratio. Possible values:
+
+@table @samp
+@item disable
+Scale the video as specified and disable this feature.
+
+@item decrease
+The output video dimensions will automatically be decreased if needed.
+
+@item increase
+The output video dimensions will automatically be increased if needed.
+
+@end table
+
+One useful instance of this option is that when you know a specific device's
+maximum allowed resolution, you can use this to limit the output video to
+that, while retaining the aspect ratio. For example, device A allows
+1280x720 playback, and your video is 1920x800. Using this option (set it to
+decrease) and specifying 1280x720 to the command line makes the output
+1280x533.
+
+Please note that this is a different thing than specifying -1 for @option{w}
+or @option{h}, you still need to specify the output resolution for this option
+to work.
+
 @end table
 
 The values of the @var{w} and @var{h} options are expressions