audio/out, video/out: hide encoding VO/AO

mpv -ao help and mpv -vo help shouldn't show the encoding outputs (named
"lavc" on both cases). Also make it impossible to select these manually
when not encoding.

audio/out/ao.c

@@ -91,13 +91,14 @@ static const struct ao_driver * const audio_out_drivers[] = {
 
 void list_audio_out(void)
 {
-    int i=0;
     mp_tmsg(MSGT_AO, MSGL_INFO, "Available audio output drivers:\n");
     mp_msg(MSGT_IDENTIFY, MSGL_INFO, "ID_AUDIO_OUTPUTS\n");
-    while (audio_out_drivers[i]) {
+    for (int i = 0; audio_out_drivers[i]; i++) {
-        const ao_info_t *info = audio_out_drivers[i++]->info;
+        const ao_info_t *info = audio_out_drivers[i]->info;
-        mp_msg(MSGT_GLOBAL, MSGL_INFO, "\t%s\t%s\n", info->short_name,
+        if (!audio_out_drivers[i]->encode) {
-               info->name);
+            mp_msg(MSGT_GLOBAL, MSGL_INFO, "\t%s\t%s\n",
+                   info->short_name, info->name);
+        }
     }
     mp_msg(MSGT_GLOBAL, MSGL_INFO,"\n");
 }
@@ -110,6 +111,13 @@ struct ao *ao_create(struct MPOpts *opts, struct input_ctx *input)
     return r;
 }
 
+static bool ao_try_init(struct ao *ao, char *params)
+{
+    if (ao->driver->encode != !!ao->encode_lavc_ctx)
+        return false;
+    return ao->driver->init(ao, params) >= 0;
+}
+
 void ao_init(struct ao *ao, char **ao_list)
 {
     /* Caller adding child blocks is not supported as we may call
@@ -148,7 +156,7 @@ void ao_init(struct ao *ao, char **ao_list)
         if (audio_out) {
             // name matches, try it
             ao->driver = audio_out;
-            if (audio_out->init(ao, params) >= 0) {
+            if (ao_try_init(ao, params)) {
                 ao->driver = audio_out;
                 ao->initialized = true;
                 return;
@@ -167,13 +175,14 @@ void ao_init(struct ao *ao, char **ao_list)
  try_defaults:
     mp_tmsg(MSGT_AO, MSGL_V, "Trying every known audio driver...\n");
 
+    ao->probing = false;
+
     // now try the rest...
     for (int i = 0; audio_out_drivers[i]; i++) {
         const struct ao_driver *audio_out = audio_out_drivers[i];
         ao->driver = audio_out;
         ao->probing = true;
-        if (audio_out->init(ao, NULL) >= 0) {
+        if (ao_try_init(ao, NULL)) {
-            ao->probing = false;
             ao->initialized = true;
             ao->driver = audio_out;
             return;

audio/out/ao.h

@@ -75,6 +75,7 @@ struct ao;
 
 struct ao_driver {
     bool is_new;
+    bool encode;
     const struct ao_info *info;
     const struct ao_old_functions *old_functions;
     int (*control)(struct ao *ao, enum aocontrol cmd, void *arg);

audio/out/ao_lavc.c

@@ -660,6 +660,7 @@ static int play(struct ao *ao, void *data, int len, int flags)
 
 const struct ao_driver audio_out_lavc = {
     .is_new = true,
+    .encode = true,
     .info = &(const struct ao_info) {
         "audio encoding using libavcodec",
         "lavc",

video/out/vo.c

@@ -131,6 +131,8 @@ const struct vo_driver *video_out_drivers[] =
 
 static int vo_preinit(struct vo *vo, char *arg)
 {
+    if (vo->driver->encode != !!vo->encode_lavc_ctx)
+        return -1;
     if (vo->driver->priv_size) {
         vo->priv = talloc_zero_size(vo, vo->driver->priv_size);
         if (vo->driver->priv_defaults)
@@ -268,12 +270,14 @@ void vo_destroy(struct vo *vo)
 
 void list_video_out(void)
 {
-    int i = 0;
     mp_tmsg(MSGT_CPLAYER, MSGL_INFO, "Available video output drivers:\n");
     mp_msg(MSGT_IDENTIFY, MSGL_INFO, "ID_VIDEO_OUTPUTS\n");
-    while (video_out_drivers[i]) {
+    for (int i = 0; video_out_drivers[i]; i++) {
-        const vo_info_t *info = video_out_drivers[i++]->info;
+        const vo_info_t *info = video_out_drivers[i]->info;
-        mp_msg(MSGT_GLOBAL, MSGL_INFO,"\t%s\t%s\n", info->short_name, info->name);
+        if (!video_out_drivers[i]->encode) {
+            mp_msg(MSGT_GLOBAL, MSGL_INFO,"\t%s\t%s\n",
+                   info->short_name, info->name);
+        }
     }
     mp_msg(MSGT_GLOBAL, MSGL_INFO,"\n");
 }

video/out/vo.h

@@ -146,6 +146,9 @@ struct vo_driver {
     // of pts values itself
     bool buffer_frames;
 
+    // Encoding functionality, which can be invoked via --o only.
+    bool encode;
+
     const vo_info_t *info;
     /*
      * Preinitializes driver (real INITIALIZATION)

video/out/vo_lavc.c

@@ -514,6 +514,7 @@ static int control(struct vo *vo, uint32_t request, void *data)
 
 const struct vo_driver video_out_lavc = {
     .buffer_frames = false,
+    .encode = true,
     .info = &(const struct vo_info_s){
         "video encoding using libavcodec",
         "lavc",