video: support positional arguments for automatic lavfi option bridge

Now e.g. --vf=pad=1000:1000 works.

All in all pretty ugly and hacky. Just look away.

DOCS/man/vf.rst

@@ -60,11 +60,11 @@ normal filter parameters.
     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.
+    tried. This bridge does not support help output, and does not verify
+    parameters before the filter is actually used. Although the mpv syntax
+    is rather similar to libavfilter's, it's not the same. (Which means not
+    everything accepted by vf_lavfi's ``graph`` option will be accepted by
+    ``--vf``.)
 
 Video filters are managed in lists. There are a few commands to manage the
 filter list.

common/av_common.c

@@ -302,6 +302,35 @@ void mp_avdict_print_unset(struct mp_log *log, int msgl, AVDictionary *dict)
         mp_msg(log, msgl, "Could not set AVOption %s='%s'\n", t->key, t->value);
 }
 
+// If the name starts with "@", try to interpret it as a number, and set *name
+// to the name of the n-th parameter.
+static void resolve_positional_arg(void *avobj, char **name)
+{
+    if (!*name || (*name)[0] != '@')
+        return;
+
+    char *end = NULL;
+    int pos = strtol(*name + 1, &end, 10);
+    if (!end || *end)
+        return;
+
+    const AVOption *opt = NULL;
+    int offset = -1;
+    while (1) {
+        opt = av_opt_next(avobj, opt);
+        if (!opt)
+            return;
+        // This is what libavfilter's parser does to skip aliases.
+        if (opt->offset != offset && opt->type != AV_OPT_TYPE_CONST)
+            pos--;
+        if (pos < 0) {
+            *name = (char *)opt->name;
+            return;
+        }
+        offset = opt->offset;
+    }
+}
+
 // kv is in the format as by OPT_KEYVALUELIST(): kv[0]=key0, kv[1]=val0, ...
 // Set these options on given avobj (using av_opt_set..., meaning avobj must
 // point to a struct that has AVClass as first member).
@@ -313,6 +342,7 @@ int mp_set_avopts(struct mp_log *log, void *avobj, char **kv)
     for (int n = 0; kv && kv[n * 2]; n++) {
         char *k = kv[n * 2 + 0];
         char *v = kv[n * 2 + 1];
+        resolve_positional_arg(avobj, &k);
         int r = av_opt_set(avobj, k, v, AV_OPT_SEARCH_CHILDREN);
         if (r == AVERROR_OPTION_NOT_FOUND) {
             mp_err(log, "AVOption '%s' not found.\n", k);

options/m_option.c

@@ -2606,17 +2606,33 @@ static void copy_obj_settings_list(const m_option_t *opt, void *dst,
 static int get_obj_param(struct mp_log *log, bstr opt_name, bstr obj_name,
                          struct m_config *config, bstr name, bstr val,
                          int flags, bool nopos,
-                         int *nold, bstr *out_name, bstr *out_val)
+                         int *nold, bstr *out_name, bstr *out_val,
+                         char *tmp, size_t tmp_size)
 {
     int r;
 
     if (!config) {
-        *out_name = name; // preserve args for opengl-hq legacy handling
-        *out_val = val;
+        // Duplicates the logic below, but with unknown parameter types/names.
+        if (val.start || nopos) {
+            *out_name = name;
+            *out_val = val;
+        } else {
+            val = name;
+            // positional fields
+            if (val.len == 0) { // Empty field, count it and go on
+                (*nold)++;
+                return 0;
+            }
+            // Positional naming convention for/followed by mp_set_avopts().
+            snprintf(tmp, tmp_size, "@%d", *nold);
+            *out_name = bstr0(tmp);
+            *out_val = val;
+            (*nold)++;
+        }
         return 1;
     }
 
-    // va.start != NULL => of the form name=val (not positional)
+    // val.start != NULL => of the form name=val (not positional)
     // If it's just "name", and the associated option exists and is a flag,
     // don't accept it as positional argument.
     if (val.start || m_config_option_requires_param(config, name) == 0 || nopos) {
@@ -2683,6 +2699,7 @@ static int m_obj_parse_sub_config(struct mp_log *log, struct bstr opt_name,
     char **args = NULL;
     int num_args = 0;
     int r = 1;
+    char tmp[80];
 
     if (ret) {
         args = *ret;
@@ -2708,7 +2725,7 @@ static int m_obj_parse_sub_config(struct mp_log *log, struct bstr opt_name,
         if (bstr_equals0(fname, "help"))
             goto print_help;
         r = get_obj_param(log, opt_name, name, config, fname, fval, flags,
-                          nopos, &nold, &fname, &fval);
+                          nopos, &nold, &fname, &fval, tmp, sizeof(tmp));
         if (r < 0)
             goto exit;
 

video/filter/vf_lavfi.c

@@ -172,7 +172,7 @@ static bool recreate_graph(struct vf_instance *vf, struct mp_image_params *fmt)
         if (!filter)
             goto error;
 
-        if (mp_set_avopts(vf->log, filter, p->cfg_filter_opts) < 0)
+        if (mp_set_avopts(vf->log, filter->priv, p->cfg_filter_opts) < 0)
             goto error;
 
         if (avfilter_init_str(filter, NULL) < 0)