Update public FFmpeg header files from r16647 to r18286.

third_party/ffmpeg/include/libavutil/base64.h

 /*
- * Base64.c
  * Copyright (c) 2006 Ryan Martell. (rdm4@martellventures.com)
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #ifndef AVUTIL_BASE64_H
 #define AVUTIL_BASE64_H
 
 #include <stdint.h>
 
 /**
- * decodes base64
- * param order as strncpy()
+ * Decodes the base64-encoded string in \p in and puts the decoded
+ * data in \p out.
+ *
+ * @param out_size size in bytes of the \p out buffer, it should be at
+ * least 3/4 of the length of \p in
+ * @return the number of bytes written, or a negative value in case of
+ * error
  */
-int av_base64_decode(uint8_t * out, const char *in, int out_length);
+int av_base64_decode(uint8_t *out, const char *in, int out_size);
 
 /**
- * encodes base64
- * @param src data, not a string
- * @param buf output string
+ * Encodes in base64 the data in \p in and puts the resulting string
+ * in \p out.
+ *
+ * @param out_size size in bytes of the \p out string, it should be at
+ * least ((\p in_size + 2) / 3) * 4 + 1
+ * @param in_size size in bytes of the \p in buffer
+ * @return the string containing the encoded data, or NULL in case of
+ * error
  */
-char *av_base64_encode(char * buf, int buf_len, const uint8_t * src, int len);
+char *av_base64_encode(char *out, int out_size, const uint8_t *in, int in_size);
 
 #endif /* AVUTIL_BASE64_H */