This only supports one device globally, but more can be used by passing them with input streams in hw_frames_ctx or by deriving new devices inside a filter graph with hwmap.
(cherry picked from commit e669db76108de8d7a36c2274c99da82cc94d1dd1)
7ce4709 ffmpeg: Support setting the hardware device to use when filtering
doc/ffmpeg.texi | 11 +++++++++++
ffmpeg.h | 1 +
ffmpeg_filter.c | 10 ++++++++--
ffmpeg_opt.c | 17 +++++++++++++++++
4 files changed, 37 insertions(+), 2 deletions(-)