vcap/screen_avf: set device d=100 if unspec

Otherwise d=0 would be initialized implicitly, which isn't screen cap
device but rather FaceTime HD Camera or so.

src/video_capture/screen_avf.c

@@ -79,12 +79,51 @@ vidcap_screen_avf_probe(struct device_info **available_cards, int *count,
         }
 }
 
+/// @returns whether the config string contains device spec (d=/uid=/name=)
+static bool
+contains_dev_spec(const char *fmt)
+{
+        char *cpy     = strdup(fmt);
+        char *tmp     = cpy;
+        char *saveptr = nullptr;
+        char *item    = nullptr;
+        while ((item = strtok_r(tmp, ":", &saveptr)) != nullptr) {
+                tmp = nullptr;
+                char *delim = strchr(item, '=');
+                if (!delim) {
+                        continue;
+                }
+                *delim = '\0';
+                if (strstr(item, "device") == item ||
+                    strstr(item, "uid") == item ||
+                    strstr(item, "name") == item) {
+                        return true;
+                }
+        }
+        return false;
+}
+
 static int
 vidcap_screen_avf_init(struct vidcap_params *params, void **state)
 {
-        if (avfoundation_usage(vidcap_params_get_fmt(params), true)) {
+        const char *fmt = vidcap_params_get_fmt(params);
+
+        if (avfoundation_usage(fmt, true)) {
                 return VIDCAP_INIT_NOERR; // help shown
         }
+
+        if (contains_dev_spec(fmt)) {
+                return vidcap_avfoundation_info.init(params, state);
+        }
+
+        // add "d=100" to initialize first screen cap av foundation device
+        const size_t orig_len = strlen(fmt);
+        const size_t new_len  = orig_len + 50;
+        char        *new_fmt  = malloc(new_len);
+        (void) snprintf(new_fmt, new_len, "%s%sd=%u", fmt,
+                        orig_len == 0 ? "" : ":", AVF_SCR_CAP_OFF);
+        vidcap_params_replace_fmt(params, new_fmt);
+        free(new_fmt);
         return vidcap_avfoundation_info.init(params, state);
 }
 

src/video_capture_params.cpp

@@ -5,7 +5,7 @@
  * @ingroup vidcap
  */
 /*
- * Copyright (c) 2013-2025 CESNET, zájmové sdružení právnických osob
+ * Copyright (c) 2013-2026 CESNET, zájmové sdružení právnických osob
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -280,6 +280,13 @@ struct vidcap_params *vidcap_params_copy(const struct vidcap_params *params)
         return ret;
 }
 
+void
+vidcap_params_replace_fmt(struct vidcap_params *params, const char *new_fmt)
+{
+        free(params->fmt);
+        params->fmt = strdup(new_fmt);
+}
+
 /**
  * Frees all members of the given structure as well as its members.
  *

src/video_capture_params.h

@@ -10,7 +10,7 @@
  * individual devices' parameters (namely per-device capture filter).
  */
 /**
- * Copyright (c) 2013-2025 CESNET, zájmové sdružení právnických osob
+ * Copyright (c) 2013-2026 CESNET, zájmové sdružení právnických osob
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -81,6 +81,8 @@ void                  vidcap_params_add_capture_filter(struct vidcap_params *par
 const char           *vidcap_params_get_capture_filter(const struct vidcap_params *params);
 void                  vidcap_params_set_flags(struct vidcap_params *params, unsigned int flags);
 void                  vidcap_params_add_flags(struct vidcap_params *params, unsigned int flags);
+void                  vidcap_params_replace_fmt(struct vidcap_params *params,
+                                                const char           *new_fmt);
 /// @}
 
 #ifdef __cplusplus