And document both `draw` and `alpha`.
9b2c57b drawtext: Add an alpha option
doc/filters.texi | 11 +++++++++++
libavfilter/vf_drawtext.c | 48 +++++++++++++++++++++++++++++++++++----------
2 files changed, 49 insertions(+), 10 deletions(-)
Upstream: git.libav.org