command: whitelist some blocking accesses for certain demuxers/streams

The properties/commands touched in this commit are all for obscure
special inputs (BD/DVD/DVB/TV), and they all block on the demuxer/stream
layer. For network streams, this blocking is very unwelcome. They will
affect playback and probably introduce pauses and frame drops. The
player can even freeze fully, and the logic that tries to make playback
abortable even if frozen complicates the player.

Since the mentioned accesses are not needed for network streams, but
they will block on network streams even though they're going to fail,
add a flag that coarsely enables/disables these accesses. Essentially it
establishes a whitelist of demuxers/streams which support them.

In theory you could to access BD/DVD images over network (or add such
support, I don't think it's a thing in mpv). In these cases these
controls still can block and could even "freeze" the player completely.

Writing to the "program" and "cache-size" properties still can block
even for network streams. Just don't use them if you don't want freezes.

demux/demux.c

@@ -2211,6 +2211,7 @@ static struct demuxer *open_given_type(struct mpv_global *global,
         .access_references = opts->access_references,
         .events = DEMUX_EVENT_ALL,
         .duration = -1,
+        .extended_ctrls = stream->extended_ctrls,
     };
     demuxer->seekable = stream->seekable;
     if (demuxer->stream->underlying && !demuxer->stream->underlying->seekable)

demux/demux.h

@@ -202,6 +202,7 @@ typedef struct demuxer {
     bool fully_read;
     bool is_network; // opened directly from a network stream
     bool access_references; // allow opening other files/URLs
+    bool extended_ctrls; // supports some of BD/DVD/DVB/TV controls
 
     // Bitmask of DEMUX_EVENT_*
     int events;

demux/demux_disc.c

@@ -342,6 +342,8 @@ static int d_open(demuxer_t *demuxer, enum demux_check check)
     if (stream_control(demuxer->stream, STREAM_CTRL_GET_TIME_LENGTH, &len) >= 1)
         demuxer->duration = len;
 
+    demuxer->extended_ctrls = true;
+
     return 0;
 }
 

demux/demux_tv.c

@@ -181,6 +181,8 @@ no_audio:
         if(funcs->control(tvh->priv,TVI_CONTROL_VID_SET_GAIN,&tvh->tv_param->gain)!=TVI_CONTROL_TRUE)
             MP_WARN(tvh, "Unable to set gain control!\n");
 
+    demuxer->extended_ctrls = true;
+
     return 0;
 }