From c365e2f7b17e6a890827802e063b823bf6e4385f Mon Sep 17 00:00:00 2001
From: Andreas Klauer <Andreas.Klauer@metamorpher.de>
Date: Fri, 27 Sep 2024 19:35:37 +0200
Subject: [PATCH] misc/random: seed using libavutil/random_seed

When starting multiple processes of `mpv --shuffle` in parallel,
sometimes the random seed happens to be identical, so files are
played in the same random order.

mp_rand_seed(0) now uses a random seed provided by libavutil,
and only falls back to time in case of failure.
---
 misc/random.c | 13 +++++++++++++
 misc/random.h |  2 +-
 osdep/timer.c |  2 --
 player/main.c |  2 ++
 4 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/misc/random.c b/misc/random.c
index d40474bee6..83cf0a727e 100644
--- a/misc/random.c
+++ b/misc/random.c
@@ -20,7 +20,10 @@
 
 #include <stdint.h>
 
+#include <libavutil/random_seed.h>
+
 #include "osdep/threads.h"
+#include "osdep/timer.h"
 #include "random.h"
 
 static uint64_t state[4];
@@ -44,6 +47,16 @@ void mp_rand_seed(uint64_t seed)
 #ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
     seed = 42;
 #endif
+
+    if (seed == 0) {
+        uint8_t buf[sizeof(seed)];
+        if (av_random_bytes(buf, sizeof(buf)) < 0) {
+            seed = mp_raw_time_ns();
+        } else {
+            memcpy(&seed, buf, sizeof(seed));
+        }
+    }
+
     mp_mutex_lock(&state_mutex);
     state[0] = seed;
     for (int i = 1; i < 4; i++)
diff --git a/misc/random.h b/misc/random.h
index dae66a0939..23b4f82399 100644
--- a/misc/random.h
+++ b/misc/random.h
@@ -24,7 +24,7 @@
 
 /*
  * Initialize the pseudo-random number generator's state with
- * the given 64-bit seed.
+ * the given 64-bit seed. If the seed is 0, it is randomized.
  */
 void mp_rand_seed(uint64_t seed);
 
diff --git a/osdep/timer.c b/osdep/timer.c
index 86cfaebf88..c0aac8972b 100644
--- a/osdep/timer.c
+++ b/osdep/timer.c
@@ -22,7 +22,6 @@
 
 #include "common/common.h"
 #include "common/msg.h"
-#include "misc/random.h"
 #include "threads.h"
 #include "timer.h"
 
@@ -32,7 +31,6 @@ static mp_once timer_init_once = MP_STATIC_ONCE_INITIALIZER;
 static void do_timer_init(void)
 {
     mp_raw_time_init();
-    mp_rand_seed(mp_raw_time_ns());
     raw_time_offset = mp_raw_time_ns();
     assert(raw_time_offset > 0);
 }
diff --git a/player/main.c b/player/main.c
index 21478a6e5f..8ed0f4d94d 100644
--- a/player/main.c
+++ b/player/main.c
@@ -30,6 +30,7 @@
 #include "mpv_talloc.h"
 
 #include "misc/dispatch.h"
+#include "misc/random.h"
 #include "misc/thread_pool.h"
 #include "osdep/io.h"
 #include "osdep/terminal.h"
@@ -263,6 +264,7 @@ struct MPContext *mp_create(void)
         talloc_enable_leak_report();
 
     mp_time_init();
+    mp_rand_seed(0);
 
     struct MPContext *mpctx = talloc(NULL, MPContext);
     *mpctx = (struct MPContext){