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 e669db76)

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:

ffmpeg.h

@@ -628,6 +628,7 @@ extern AVBufferRef *hw_device_ctx;
 #if CONFIG_QSV
 extern char *qsv_device;
 #endif
+extern HWDevice *filter_hw_device;
 
 
 void term_init(void);

ffmpeg_filter.c

@@ -1046,9 +1046,15 @@ int configure_filtergraph(FilterGraph *fg)
     if ((ret = avfilter_graph_parse2(fg->graph, graph_desc, &inputs, &outputs)) < 0)
         goto fail;
 
-    if (hw_device_ctx) {
+    if (filter_hw_device || hw_device_ctx) {
+        AVBufferRef *device = filter_hw_device ? filter_hw_device->device_ref
+                                               : hw_device_ctx;
         for (i = 0; i < fg->graph->nb_filters; i++) {
-            fg->graph->filters[i]->hw_device_ctx = av_buffer_ref(hw_device_ctx);
+            fg->graph->filters[i]->hw_device_ctx = av_buffer_ref(device);
+            if (!fg->graph->filters[i]->hw_device_ctx) {
+                ret = AVERROR(ENOMEM);
+                goto fail;
+            }
         }
     }
 

ffmpeg_opt.c

@@ -98,6 +98,7 @@ const HWAccel hwaccels[] = {
 };
 int hwaccel_lax_profile_check = 0;
 AVBufferRef *hw_device_ctx;
+HWDevice *filter_hw_device;
 
 char *vstats_filename;
 char *sdp_filename;
@@ -495,6 +496,20 @@ static int opt_init_hw_device(void *optctx, const char *opt, const char *arg)
     }
 }
 
+static int opt_filter_hw_device(void *optctx, const char *opt, const char *arg)
+{
+    if (filter_hw_device) {
+        av_log(NULL, AV_LOG_ERROR, "Only one filter device can be used.\n");
+        return AVERROR(EINVAL);
+    }
+    filter_hw_device = hw_device_get_by_name(arg);
+    if (!filter_hw_device) {
+        av_log(NULL, AV_LOG_ERROR, "Invalid filter device %s.\n", arg);
+        return AVERROR(EINVAL);
+    }
+    return 0;
+}
+
 /**
  * Parse a metadata specifier passed as 'arg' parameter.
  * @param arg  metadata string to parse
@@ -3708,6 +3723,8 @@ const OptionDef options[] = {
 
     { "init_hw_device", HAS_ARG | OPT_EXPERT, { .func_arg = opt_init_hw_device },
         "initialise hardware device", "args" },
+    { "filter_hw_device", HAS_ARG | OPT_EXPERT, { .func_arg = opt_filter_hw_device },
+        "set hardware device used when filtering", "device" },
 
     { NULL, },
 };