Add a centralized avcodec lock

avcodec is used from at least three different plugins: avcodec,
switcher (which seems dead though) and indirectly in avformat. We need
to have a common interlock for all of these.

include/vlc_avcodec.h

+/*****************************************************************************
+ * vlc_avcodec.h: VLC thread support for FFMPEG/libavcodec
+ *****************************************************************************
+ * Copyright (C) 2009 Rémi Denis-Courmont
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifndef VLC_AVCODEC_H
+# define VLC_AVCODEC_H 1
+
+VLC_EXPORT( void, vlc_avcodec_mutex, (bool) );
+
+static inline void vlc_avcodec_lock (void)
+{
+    vlc_avcodec_mutex (true);
+}
+
+static inline void vlc_avcodec_unlock (void)
+{
+    vlc_avcodec_mutex (false);
+}
+
+#endif

src/Makefile.am

@@ -41,6 +41,7 @@ pluginsinclude_HEADERS = \
 	../include/vlc_acl.h \
 	../include/vlc_aout.h \
 	../include/vlc_arrays.h \
+	../include/vlc_avcodec.h \
 	../include/vlc_bits.h \
 	../include/vlc_block.h \
 	../include/vlc_block_helper.h \

src/libvlc.c

@@ -2130,3 +2130,15 @@ static void InitDeviceValues( libvlc_int_t *p_vlc )
     (void)p_vlc;
 #endif /* HAVE_HAL */
 }
+
+#include <vlc_avcodec.h>
+
+void vlc_avcodec_mutex (bool acquire)
+{
+    static vlc_mutex_t lock = VLC_STATIC_MUTEX;
+
+    if (acquire)
+        vlc_mutex_lock (&lock);
+    else
+        vlc_mutex_unlock (&lock);
+}

src/libvlccore.sym

@@ -409,6 +409,7 @@ var_SetChecked
 __var_TriggerCallback
 __var_Type
 video_format_FixRgb
+vlc_avcodec_mutex
 vlc_b64_decode
 vlc_b64_decode_binary
 vlc_b64_decode_binary_to_buffer