msg: add --log-file option

This allows getting the log at all with --no-terminal and without having
to retrieve log messages manually with the client API. The log level is
hardcoded to -v. A higher log level would lead to too much log output
(huge file sizes and latency issues due to waiting on the disk), and
isn't too useful in general anyway. For debugging, the terminal can be
used instead.

DOCS/man/options.rst

@@ -443,6 +443,11 @@ Program Behavior
     ``bestvideo+bestaudio``.
     (Default: ``best``)
 
+``--log-file=<path>``
+    Opens the given path for writing, and print log messages to it. Existing
+    files will be truncated. The log level always corresponds to ``-v``,
+    regardless of terminal verbosity levels.
+
 Video
 -----
 

common/msg.c

@@ -60,6 +60,7 @@ struct mp_log_root {
     bool force_stderr;
     struct mp_log_buffer **buffers;
     int num_buffers;
+    FILE *log_file;
     FILE *stats_file;
     // --- semi-atomic access
     bool mute;
@@ -122,6 +123,8 @@ static void update_loglevel(struct mp_log *log)
     }
     for (int n = 0; n < log->root->num_buffers; n++)
         log->level = MPMAX(log->level, log->root->buffers[n]->level);
+    if (log->root->log_file)
+        log->level = MPMAX(log->level, MSGL_V);
     if (log->root->stats_file)
         log->level = MPMAX(log->level, MSGL_STATS);
     atomic_store(&log->reload_counter, atomic_load(&log->root->reload_counter));
@@ -278,6 +281,19 @@ static void print_terminal_line(struct mp_log *log, int lev, char *text)
     fflush(stream);
 }
 
+static void write_log_file(struct mp_log *log, int lev, char *text)
+{
+    struct mp_log_root *root = log->root;
+
+    if (lev > MSGL_V || !root->log_file)
+        return;
+
+    fprintf(root->log_file, "[%8.3f][%c][%s] %s",
+            (mp_time_us() - MP_START_TIME) / 1e6,
+            mp_log_levels[lev][0],
+            log->verbose_prefix, text);
+}
+
 static void write_msg_to_buffers(struct mp_log *log, int lev, char *text)
 {
     struct mp_log_root *root = log->root;
@@ -356,6 +372,7 @@ void mp_msg_va(struct mp_log *log, int lev, const char *format, va_list va)
             char saved = next[0];
             next[0] = '\0';
             print_terminal_line(log, lev, text);
+            write_log_file(log, lev, text);
             write_msg_to_buffers(log, lev, text);
             next[0] = saved;
             text = next;
@@ -461,6 +478,9 @@ void mp_msg_update_msglevels(struct mpv_global *global)
     talloc_free(root->msglevels);
     root->msglevels = talloc_strdup(root, global->opts->msglevels);
 
+    if (!root->log_file && opts->log_file && opts->log_file[0])
+        root->log_file = fopen(opts->log_file, "wb");
+
     atomic_fetch_add(&root->reload_counter, 1);
     pthread_mutex_unlock(&mp_msg_lock);
 }
@@ -484,6 +504,8 @@ void mp_msg_uninit(struct mpv_global *global)
     struct mp_log_root *root = global->log->root;
     if (root->stats_file)
         fclose(root->stats_file);
+    if (root->log_file)
+        fclose(root->log_file);
     talloc_free(root);
     global->log = NULL;
 }

options/options.c

@@ -109,6 +109,7 @@ const m_option_t mp_opts[] = {
                 .type = &m_option_type_msglevels),
     OPT_STRING("dump-stats", dump_stats, CONF_GLOBAL | CONF_PRE_PARSE),
     OPT_FLAG("msg-color", msg_color, CONF_GLOBAL | CONF_PRE_PARSE),
+    OPT_STRING("log-file", log_file, CONF_GLOBAL | CONF_PRE_PARSE),
     OPT_FLAG("msg-module", msg_module, CONF_GLOBAL),
     OPT_FLAG("msg-time", msg_time, CONF_GLOBAL),
 #ifdef _WIN32

options/options.h

@@ -60,6 +60,7 @@ typedef struct MPOpts {
     int msg_color;
     int msg_module;
     int msg_time;
+    char *log_file;
 
     char **reset_options;
     char **script_files;

osdep/timer.c

@@ -38,7 +38,7 @@ static void do_timer_init(void)
     // Arbitrary additional offset to avoid confusing relative/absolute times.
     // Also,we rule that the timer never returns 0 (so default-initialized
     // time values will be always in the past).
-    raw_time_offset -= 10000000;
+    raw_time_offset -= MP_START_TIME;
 }
 
 void mp_time_init(void)

osdep/timer.h

@@ -38,6 +38,8 @@ uint64_t mp_raw_time_us(void);
 // Sleep in microseconds.
 void mp_sleep_us(int64_t us);
 
+#define MP_START_TIME 10000000
+
 // Return the amount of time that has passed since the last call, in
 // microseconds. *t is used to calculate the time that has passed by storing
 // the current time in it. If *t is 0, the call will return 0. (So that the