msg: add --msgtime option to add timestamps to each output message

Will be helpful to track down strange wait times and such issues, as
well when you have develop something timing related. (Then you may print
timestamps in your debug output, and the --msgtime timestamps will help
giving context.)

common/msg.c

@@ -34,6 +34,7 @@
 #include "options/options.h"
 #include "osdep/terminal.h"
 #include "osdep/io.h"
+#include "osdep/timer.h"
 
 #include "msg.h"
 #include "msg_control.h"
@@ -48,6 +49,7 @@ struct mp_log_root {
     bool use_terminal;  // make accesses to stderr/stdout
     bool smode;         // slave mode compatibility glue
     bool module;
+    bool show_time;
     bool termosd;       // use terminal control codes for status line
     bool header;        // indicate that message header should be printed
     int blank_lines;    // number of lines useable by status
@@ -241,8 +243,12 @@ static void print_msg_on_terminal(struct mp_log *log, int lev, char *text)
         set_msg_color(stream, lev);
 
     do {
-        if (header && prefix)
-            fprintf(stream, "[%s] ", prefix);
+        if (header) {
+            if (root->show_time)
+                fprintf(stream, "[%" PRId64 "] ", mp_time_us());
+            if (prefix)
+                fprintf(stream, "[%s] ", prefix);
+        }
 
         char *next = strchr(text, '\n');
         int len = next ? next - text + 1 : strlen(text);
@@ -378,6 +384,7 @@ void mp_msg_update_msglevels(struct mpv_global *global)
     root->module = opts->msg_module;
     root->smode = opts->msg_identify;
     root->use_terminal = opts->use_terminal;
+    root->show_time = opts->msg_time;
     if (root->use_terminal) {
         root->color = opts->msg_color && isatty(fileno(stdout));
         root->termosd = !opts->slave_mode && isatty(fileno(stderr));

options/options.c

@@ -232,6 +232,7 @@ const m_option_t mp_opts[] = {
                 .type = &m_option_type_msglevels),
     OPT_FLAG("msgcolor", msg_color, CONF_GLOBAL | CONF_PRE_PARSE),
     OPT_FLAG("msgmodule", msg_module, CONF_GLOBAL),
+    OPT_FLAG("msgtime", msg_time, CONF_GLOBAL),
     OPT_FLAG("identify", msg_identify, CONF_GLOBAL),
 #if HAVE_PRIORITY
     {"priority", &proc_priority, CONF_TYPE_STRING, 0, 0, 0, NULL},

options/options.h

@@ -50,6 +50,7 @@ typedef struct MPOpts {
     int msg_identify;
     int msg_color;
     int msg_module;
+    int msg_time;
 
     char **reset_options;
     char **lua_files;