Update public FFmpeg header files from r16647 to r18286.

third_party/ffmpeg/include/libavutil/avstring.h

 /*
  * Copyright (c) 2007 Mans Rullgard
  *
  * 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.
  *
@@ skipping 11 matching lines @@
 #define AVUTIL_AVSTRING_H
 
 #include <stddef.h>
 
 /**
  * Return non-zero if pfx is a prefix of str. If it is, *ptr is set to
  * the address of the first character in str after the prefix.
  *
  * @param str input string
  * @param pfx prefix to test
- * @param ptr updated after the prefix in str in there is a match
+ * @param ptr updated if the prefix is matched inside str
  * @return non-zero if the prefix matches, zero otherwise
  */
 int av_strstart(const char *str, const char *pfx, const char **ptr);
 
 /**
  * Return non-zero if pfx is a prefix of str independent of case. If
  * it is, *ptr is set to the address of the first character in str
  * after the prefix.
  *
  * @param str input string
  * @param pfx prefix to test
- * @param ptr updated after the prefix in str in there is a match
+ * @param ptr updated if the prefix is matched inside str
  * @return non-zero if the prefix matches, zero otherwise
  */
 int av_stristart(const char *str, const char *pfx, const char **ptr);
 
 /**
  * Copy the string src to dst, but no more than size - 1 bytes, and
- * null terminate dst.
+ * null-terminate dst.
  *
  * This function is the same as BSD strlcpy().
  *
  * @param dst destination buffer
  * @param src source string
  * @param size size of destination buffer
  * @return the length of src
  */
 size_t av_strlcpy(char *dst, const char *src, size_t size);
 
 /**
  * Append the string src to the string dst, but to a total length of
- * no more than size - 1 bytes, and null terminate dst.
+ * no more than size - 1 bytes, and null-terminate dst.
  *
  * This function is similar to BSD strlcat(), but differs when
  * size <= strlen(dst).
  *
  * @param dst destination buffer
  * @param src source string
  * @param size size of destination buffer
  * @return the total length of src and dst
  */
 size_t av_strlcat(char *dst, const char *src, size_t size);
 
 /**
  * Append output to a string, according to a format. Never write out of
  * the destination buffer, and and always put a terminating 0 within
  * the buffer.
  * @param dst destination buffer (string to which the output is
  *  appended)
  * @param size total size of the destination buffer
  * @param fmt printf-compatible format string, specifying how the
  *  following parameters are used
  * @return the length of the string that would have been generated
  *  if enough space had been available
  */
 size_t av_strlcatf(char *dst, size_t size, const char *fmt, ...);
 
 #endif /* AVUTIL_AVSTRING_H */