options: enable tls-verify by default

We shouldn't default to no verification in current year. User can
opt-out if needed.

Keep it disable for builds without libcurl when libavformat is older
than 63.0.100. This is done to match ffmpeg's timeline for enabling
tls_verify by default in lavf, also to ensure we the default verify
locations will be loaded on such version.

DOCS/interface-changes/tls-verify-default.txt

@@ -0,0 +1 @@
+change `--tls-verify` default to `yes`

DOCS/man/options.rst

@@ -5663,9 +5663,16 @@ Network
     Certificate authority database file for use with TLS. (Silently fails with
     older FFmpeg versions.)
 
-``--tls-verify``
-    Verify peer certificates when using TLS (e.g. with ``https://...``).
-    (Silently fails with older FFmpeg versions.)
+``--tls-verify=<yes|no>``
+    Verify peer certificates when using TLS (e.g. with ``https://...``)
+    (default: yes*). Disabling this option allows man-in-the-middle attacks
+    to silently substitute the content of an HTTPS stream and is only
+    recommended as a per-stream override when verification fails for a
+    known-good reason (e.g. an outdated CA bundle, a corporate proxy, a
+    development server with a self-signed certificate).
+
+    This is disabled by default, if mpv is built without libcurl and
+    libavformat is older than 63.0.100.
 
 ``--tls-cert-file``
     A file containing a certificate to use in the handshake with the

stream/network.c

@@ -17,6 +17,8 @@
 
 #include <float.h>
 
+#include <libavformat/version.h>
+
 #include "network.h"
 #include "options/m_option.h"
 
@@ -41,5 +43,8 @@ const struct m_sub_options mp_network_conf = {
     .defaults = &(const struct mp_network_opts){
         .useragent = "libmpv",
         .timeout = 60,
+#if HAVE_LIBCURL || LIBAVFORMAT_VERSION_MAJOR >= 63
+        .tls_verify = true,
+#endif
     },
 };