ffmpeg: Support setting the hardware device to use when filtering

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)

1 files changed, 11 insertions, 0 deletions

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index db7f05a3e0..4616a4239e 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -765,6 +765,17 @@ deriving it from the existing device with the name @var{source}.
 @item -init_hw_device list
 List all hardware device types supported in this build of ffmpeg.
 
+@item -filter_hw_device @var{name}
+Pass the hardware device called @var{name} to all filters in any filter graph.
+This can be used to set the device to upload to with the @code{hwupload} filter,
+or the device to map to with the @code{hwmap} filter.  Other filters may also
+make use of this parameter when they require a hardware device.  Note that this
+is typically only required when the input is not already in hardware frames -
+when it is, filters will derive the device they require from the context of the
+frames they receive as input.
+
+This is a global setting, so all filters will receive the same device.
+
 @item -hwaccel[:@var{stream_specifier}] @var{hwaccel} (@emph{input,per-stream})
 Use hardware acceleration to decode the matching stream(s). The allowed values
 of @var{hwaccel} are: