video: add automatic libavfilter bridge to option parsing

Now you can for example do "--vf=hue=h=60" - there is no "hue" filter in
mpv, so libavfilter's will be used.

This has certain caveats (see manpage).

The point of this is providing a relatively smooth transition path to
removing our own filter stuff.

DOCS/man/vf.rst

@@ -59,6 +59,13 @@ normal filter parameters.
     in mpv (such as filters which deal with mpv specifics, or which are
     implemented in mpv only).
 
+    If a filter is not builtin, the ``lavfi-bridge`` will be automatically
+    tried. Keep in mind that this filter does not support positional arguments
+    like ``--vf=name=arg1:arg2``. Instead, you must use
+    ``--vf=name=arg1name=arg1value:...``. This bridge also does not support
+    help output, and does not verify parameters before the filter is actually
+    used.
+
 Video filters are managed in lists. There are a few commands to manage the
 filter list.
 

video/filter/vf.c

@@ -56,6 +56,7 @@ extern const vf_info_t vf_info_yadif;
 extern const vf_info_t vf_info_stereo3d;
 extern const vf_info_t vf_info_dlopen;
 extern const vf_info_t vf_info_lavfi;
+extern const vf_info_t vf_info_lavfi_bridge;
 extern const vf_info_t vf_info_vaapi;
 extern const vf_info_t vf_info_vapoursynth;
 extern const vf_info_t vf_info_vapoursynth_lazy;
@@ -74,6 +75,7 @@ static const vf_info_t *const filter_list[] = {
 
     &vf_info_mirror,
     &vf_info_lavfi,
+    &vf_info_lavfi_bridge,
     &vf_info_rotate,
     &vf_info_gradfun,
     &vf_info_pullup,
@@ -129,6 +131,7 @@ const struct m_obj_list vf_obj_list = {
     .get_desc = get_desc,
     .description = "video filters",
     .allow_disable_entries = true,
+    .allow_unknown_entries = true,
 };
 
 // Try the cmd on each filter (starting with the first), and stop at the first
@@ -241,10 +244,17 @@ void vf_print_filter_chain(struct vf_chain *c, int msglevel,
 static struct vf_instance *vf_open(struct vf_chain *c, const char *name,
                                    char **args)
 {
+    const char *lavfi_name = NULL;
+    char **lavfi_args = NULL;
     struct m_obj_desc desc;
     if (!m_obj_list_find(&desc, &vf_obj_list, bstr0(name))) {
-        MP_ERR(c, "Couldn't find video filter '%s'.\n", name);
+        if (!m_obj_list_find(&desc, &vf_obj_list, bstr0("lavfi-bridge"))) {
-        return NULL;
+            MP_ERR(c, "Couldn't find video filter '%s'.\n", name);
+            return NULL;
+        }
+        lavfi_name = name;
+        lavfi_args = args;
+        args = NULL;
     }
     vf_instance_t *vf = talloc_zero(NULL, struct vf_instance);
     *vf = (vf_instance_t) {
@@ -260,6 +270,19 @@ static struct vf_instance *vf_open(struct vf_chain *c, const char *name,
                                         name, c->opts->vf_defs, args);
     if (!config)
         goto error;
+    if (lavfi_name) {
+        // Pass the filter arguments as proper sub-options to the bridge filter.
+        struct m_config_option *name_opt = m_config_get_co(config, bstr0("name"));
+        assert(name_opt);
+        assert(name_opt->opt->type == &m_option_type_string);
+        if (m_config_set_option_raw(config, name_opt, &lavfi_name, 0) < 0)
+            goto error;
+        struct m_config_option *opts = m_config_get_co(config, bstr0("opts"));
+        assert(opts);
+        assert(opts->opt->type == &m_option_type_keyvalue_list);
+        if (m_config_set_option_raw(config, opts, &lavfi_args, 0) < 0)
+            goto error;
+    }
     vf->priv = config->optstruct;
     int retcode = vf->info->open(vf);
     if (retcode < 1)

video/filter/vf_lavfi.c

@@ -65,6 +65,9 @@
 #endif
 
 struct vf_priv_s {
+    // Single filter bridge, instead of a graph.
+    bool is_bridge;
+
     AVFilterGraph *graph;
     AVFilterContext *in;
     AVFilterContext *out;
@@ -86,10 +89,9 @@ struct vf_priv_s {
     char *cfg_graph;
     int64_t cfg_sws_flags;
     char **cfg_avopts;
-};
 
-static const struct vf_priv_s vf_priv_dflt = {
+    char *cfg_filter_name;
-    .cfg_sws_flags = SWS_BICUBIC,
+    char **cfg_filter_opts;
 };
 
 static void destroy_graph(struct vf_instance *vf)
@@ -113,13 +115,12 @@ static bool recreate_graph(struct vf_instance *vf, struct mp_image_params *fmt)
     AVFilterContext *in = NULL, *out = NULL;
     int ret;
 
-    if (bstr0(p->cfg_graph).len == 0) {
+    if (!p->is_bridge && bstr0(p->cfg_graph).len == 0) {
         MP_FATAL(vf, "lavfi: no filter graph set\n");
         return false;
     }
 
     destroy_graph(vf);
-    MP_VERBOSE(vf, "lavfi: create graph: '%s'\n", p->cfg_graph);
 
     AVFilterGraph *graph = avfilter_graph_alloc();
     if (!graph)
@@ -165,14 +166,46 @@ static bool recreate_graph(struct vf_instance *vf, struct mp_image_params *fmt)
                                      "out", NULL, NULL, graph) < 0)
         goto error;
 
-    outputs->name    = av_strdup("in");
+    if (p->is_bridge) {
-    outputs->filter_ctx = in;
+        AVFilterContext *filter = avfilter_graph_alloc_filter(graph,
+                        avfilter_get_by_name(p->cfg_filter_name), "filter");
+        if (!filter)
+            goto error;
 
-    inputs->name    = av_strdup("out");
+        if (mp_set_avopts(vf->log, filter, p->cfg_filter_opts) < 0)
-    inputs->filter_ctx = out;
+            goto error;
 
-    if (graph_parse(graph, p->cfg_graph, inputs, outputs, NULL) < 0)
+        if (avfilter_init_str(filter, NULL) < 0)
-        goto error;
+            goto error;
+
+        // Yep, we have to manually link those filters.
+        if (filter->nb_inputs != 1 ||
+            avfilter_pad_get_type(filter->input_pads, 0) != AVMEDIA_TYPE_VIDEO ||
+            filter->nb_outputs != 1 ||
+            avfilter_pad_get_type(filter->output_pads, 0) != AVMEDIA_TYPE_VIDEO)
+        {
+            MP_ERR(vf, "The filter is required to have 1 video input pad and "
+                       "1 video output pad.\n");
+            goto error;
+        }
+        if (avfilter_link(in, 0, filter, 0) < 0 ||
+            avfilter_link(filter, 0, out, 0) < 0)
+        {
+            MP_ERR(vf, "Failed to link filter.\n");
+            goto error;
+        }
+    } else {
+        MP_VERBOSE(vf, "lavfi: create graph: '%s'\n", p->cfg_graph);
+
+        outputs->name    = av_strdup("in");
+        outputs->filter_ctx = in;
+
+        inputs->name    = av_strdup("out");
+        inputs->filter_ctx = out;
+
+        if (graph_parse(graph, p->cfg_graph, inputs, outputs, NULL) < 0)
+            goto error;
+    }
 
     if (vf->hwdec_devs) {
         struct mp_hwdec_ctx *hwdec = hwdec_devices_get_first(vf->hwdec_devs);
@@ -384,6 +417,8 @@ static void uninit(struct vf_instance *vf)
 
 static int vf_open(vf_instance_t *vf)
 {
+    struct vf_priv_s *p = vf->priv;
+
     vf->reconfig = reconfig;
     vf->filter_ext = filter_ext;
     vf->filter_out = filter_out;
@@ -391,6 +426,18 @@ static int vf_open(vf_instance_t *vf)
     vf->query_format = query_format;
     vf->control = control;
     vf->uninit = uninit;
+
+    if (p->is_bridge) {
+        if (!p->cfg_filter_name) {
+            MP_ERR(vf, "Filter name not set!\n");
+            return 0;
+        }
+        if (!avfilter_get_by_name(p->cfg_filter_name)) {
+            MP_ERR(vf, "libavfilter filter '%s' not found!\n", p->cfg_filter_name);
+            return 0;
+        }
+    }
+
     return 1;
 }
 
@@ -445,11 +492,32 @@ const vf_info_t vf_info_lavfi = {
     .name = "lavfi",
     .open = vf_open,
     .priv_size = sizeof(struct vf_priv_s),
-    .priv_defaults = &vf_priv_dflt,
+    .priv_defaults = &(const struct vf_priv_s){
+        .cfg_sws_flags = SWS_BICUBIC,
+    },
     .options = vf_opts_fields,
     .print_help = print_help,
 };
 
+const vf_info_t vf_info_lavfi_bridge = {
+    .description = "libavfilter bridge (explicit options)",
+    .name = "lavfi-bridge",
+    .open = vf_open,
+    .priv_size = sizeof(struct vf_priv_s),
+    .options = (const m_option_t[]) {
+        OPT_STRING("name", cfg_filter_name, M_OPT_MIN, .min = 1),
+        OPT_KEYVALUELIST("opts", cfg_filter_opts, 0),
+        OPT_INT64("sws-flags", cfg_sws_flags, 0),
+        OPT_KEYVALUELIST("o", cfg_avopts, 0),
+        {0}
+    },
+    .priv_defaults = &(const struct vf_priv_s){
+        .is_bridge = true,
+        .cfg_sws_flags = SWS_BICUBIC,
+    },
+    .print_help = print_help,
+};
+
 // The following code is for the old filters wrapper code.
 
 struct vf_lw_opts {
@@ -497,7 +565,7 @@ int vf_lw_set_graph(struct vf_instance *vf, struct vf_lw_opts *lavfi_opts,
     void *old_priv = vf->priv;
     struct vf_priv_s *p = talloc(vf, struct vf_priv_s);
     vf->priv = p;
-    *p = vf_priv_dflt;
+    *p = *(const struct vf_priv_s *)vf_info_lavfi.priv_defaults;
     p->cfg_sws_flags = lavfi_opts->sws_flags;
     p->cfg_avopts = lavfi_opts->avopts;
     va_list ap;