libvpx: make vp8 and vp9 selectable

[ffmpeg] / doc / filters.texi

diff --git a/doc/filters.texi b/doc/filters.texi
index 55e4468fd6cafaa8bad3c27871d50736568fb63a..34db2f4630d40a64c8f899fd42af3dabce1eebae 100644 (file)
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -250,11 +250,12 @@ Maximum compensation in samples per second. Relevant only with compensate=1.
 Default value 500.
 
 @item first_pts
-Assume the first pts should be this value.
+Assume the first pts should be this value. The time base is 1 / sample rate.
 This allows for padding/trimming at the start of stream. By default, no
 assumption is made about the first frame's expected pts, so no padding or
 trimming is done. For example, this could be set to 0 to pad the beginning with
-silence if an audio stream starts after the video stream.
+silence if an audio stream starts after the video stream or to trim any samples
+with a negative pts due to encoder delay.
 
 @end table