multimedia/vmaf: unbreak legacy API consumers after 1868dedecc9a

$ aomenc --tune=vmaf --output=foo.mp4 foo.y4m
Pass 1/2 frame    1/0          0B       0 us 0.00 fpm [ETA  unknown] libvmaf ERROR could not read model from path: "/usr/local/share/model/vmaf_v0.6.1.json"
Fatal error: Failed to load VMAF model.

$ ffmpeg -i foo.y4m -i bar.y4m -lavfi libvmaf -f null -
[...]
libvmaf INFO `compute_vmaf()` is deprecated and will be removed in a future libvmaf version
libvmaf ERROR could not read model from path: "/usr/local/share/model/vmaf_v0.6.1.pkl"
libvmaf ERROR support for pkl model files has been removed, use json
libvmaf ERROR problem loading model file: /usr/local/share/model/vmaf_v0.6.1.pkl
[Parsed_libvmaf_0 @ 0x8061b3b40] libvmaf encountered an error, check log for details

(cherry picked from commit 7f163c23e1a732c8b65cb7b8ecfbcd9e8dfd1cd8)

1 files changed, 32 insertions, 0 deletions

diff --git a/multimedia/ffmpeg/files/patch-vmaf b/multimedia/ffmpeg/files/patch-vmaf
new file mode 100644
index 000000000000..b7b205fd9eb3
--- /dev/null
+++ b/multimedia/ffmpeg/files/patch-vmaf
@@ -0,0 +1,32 @@
+https://github.com/Netflix/vmaf/commit/122089fa3d23
+
+--- doc/filters.texi.orig	2021-10-24 20:47:07 UTC
++++ doc/filters.texi
+@@ -13875,14 +13875,14 @@ The obtained VMAF score is printed through the logging
+ It requires Netflix's vmaf library (libvmaf) as a pre-requisite.
+ After installing the library it can be enabled using:
+ @code{./configure --enable-libvmaf}.
+-If no model path is specified it uses the default model: @code{vmaf_v0.6.1.pkl}.
++If no model path is specified it uses the default model: @code{vmaf_v0.6.1.json}.
+ 
+ The filter has following options:
+ 
+ @table @option
+ @item model_path
+ Set the model path which is to be used for SVM.
+-Default value: @code{"/usr/local/share/model/vmaf_v0.6.1.pkl"}
++Default value: @code{"/usr/local/share/model/vmaf_v0.6.1.json"}
+ 
+ @item log_path
+ Set the file path to be used to store logs.
+--- libavfilter/vf_libvmaf.c.orig	2021-10-24 20:47:07 UTC
++++ libavfilter/vf_libvmaf.c
+@@ -72,7 +72,7 @@ typedef struct LIBVMAFContext {
+ #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
+ 
+ static const AVOption libvmaf_options[] = {
+-    {"model_path",  "Set the model to be used for computing vmaf.",                     OFFSET(model_path), AV_OPT_TYPE_STRING, {.str="/usr/local/share/model/vmaf_v0.6.1.pkl"}, 0, 1, FLAGS},
++    {"model_path",  "Set the model to be used for computing vmaf.",                     OFFSET(model_path), AV_OPT_TYPE_STRING, {.str="/usr/local/share/model/vmaf_v0.6.1.json"}, 0, 1, FLAGS},
+     {"log_path",  "Set the file path to be used to store logs.",                        OFFSET(log_path), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 1, FLAGS},
+     {"log_fmt",  "Set the format of the log (csv, json or xml).",                       OFFSET(log_fmt), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 1, FLAGS},
+     {"enable_transform",  "Enables transform for computing vmaf.",                      OFFSET(enable_transform), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},