lavfi/vf_libplacebo: allow operation without avhwdevice

Recent versions of libplacebo have required Vulkan versions incompatible
with lavu Vulkan hwcontexts. While this is expected to change
eventually, breaking vf_libplacebo every time there is such a transition
period is obviously undesired behavior, as the following sea of bug
reports shows.

This commit adds a fallback path for init_vulkan failures which simply
creates an internal device if there was no user-supplied Vulkan hwaccel.
Useful when no interop with lavu vulkan hwframes is needed or desired,
and makes using this filter easier inside certain applications.

Fixes: https://github.com/haasn/libplacebo/issues/170
Fixes: https://github.com/mpv-player/mpv/issues/9589#issuecomment-1535432185
Fixes: https://github.com/mpv-player/mpv/issues/11363
Fixes: https://github.com/mpv-player/mpv/issues/11685#issuecomment-1546627082
Closes: https://code.videolan.org/videolan/libplacebo/-/issues/270

libavfilter/vf_libplacebo.c

@@ -351,29 +351,14 @@ fail:
     return err;
 }
 
-static int init_vulkan(AVFilterContext *avctx)
+static int init_vulkan(AVFilterContext *avctx, const AVVulkanDeviceContext *hwctx)
 {
     int err = 0;
     LibplaceboContext *s = avctx->priv;
-    const AVHWDeviceContext *avhwctx;
-    const AVVulkanDeviceContext *hwctx;
     uint8_t *buf = NULL;
     size_t buf_len;
 
-    if (!avctx->hw_device_ctx) {
+    if (hwctx) {
-        av_log(s, AV_LOG_ERROR, "Missing vulkan hwdevice for vf_libplacebo.\n");
-        return AVERROR(EINVAL);
-    }
-
-    avhwctx = (AVHWDeviceContext *) avctx->hw_device_ctx->data;
-    if (avhwctx->type != AV_HWDEVICE_TYPE_VULKAN) {
-        av_log(s, AV_LOG_ERROR, "Expected vulkan hwdevice for vf_libplacebo, got %s.\n",
-            av_hwdevice_get_type_name(avhwctx->type));
-        return AVERROR(EINVAL);
-    }
-
-    hwctx = avhwctx->hwctx;
-
         /* Import libavfilter vulkan context into libplacebo */
         s->vulkan = pl_vulkan_import(s->log, pl_vulkan_import_params(
             .instance       = hwctx->inst,
@@ -398,9 +383,15 @@ static int init_vulkan(AVFilterContext *avctx)
             /* This is the highest version created by hwcontext_vulkan.c */
             .max_api_version = VK_API_VERSION_1_2,
         ));
+    } else {
+        s->vulkan = pl_vulkan_create(s->log, pl_vulkan_params(
+            .queue_count = 0, /* enable all queues for parallelization */
+        ));
+    }
 
     if (!s->vulkan) {
-        av_log(s, AV_LOG_ERROR, "Failed importing vulkan device to libplacebo!\n");
+        av_log(s, AV_LOG_ERROR, "Failed %s Vulkan device!\n",
+               hwctx ? "importing" : "creating");
         err = AVERROR_EXTERNAL;
         goto fail;
     }
@@ -695,10 +686,17 @@ static int libplacebo_query_format(AVFilterContext *ctx)
 {
     int err;
     LibplaceboContext *s = ctx->priv;
+    const AVVulkanDeviceContext *vkhwctx = NULL;
     const AVPixFmtDescriptor *desc = NULL;
     AVFilterFormats *infmts = NULL, *outfmts = NULL;
 
-    RET(init_vulkan(ctx));
+    if (ctx->hw_device_ctx) {
+        const AVHWDeviceContext *avhwctx = (void *) ctx->hw_device_ctx->data;
+        if (avhwctx->type == AV_HWDEVICE_TYPE_VULKAN)
+            vkhwctx = avhwctx->hwctx;
+    }
+
+    RET(init_vulkan(ctx, vkhwctx));
 
     while ((desc = av_pix_fmt_desc_next(desc))) {
         enum AVPixelFormat pixfmt = av_pix_fmt_desc_get_id(desc);
@@ -710,6 +708,11 @@ static int libplacebo_query_format(AVFilterContext *ctx)
             continue;
 #endif
 
+        if (pixfmt == AV_PIX_FMT_VULKAN) {
+            if (!vkhwctx || vkhwctx->act_dev != s->vulkan->device)
+                continue;
+        }
+
         if (!pl_test_pixfmt(s->gpu, pixfmt))
             continue;