diff --git a/libavutil/base64.h b/libavutil/base64.h
index 68429366c1..092980b093 100644
--- a/libavutil/base64.h
+++ b/libavutil/base64.h
@@ -24,25 +24,25 @@
 #include <stdint.h>
 
 /**
- * Decode the base64-encoded string in in and put the decoded
- * data in out.
+ * Decode a base64-encoded string.
  *
- * @param out_size size in bytes of the out buffer, it should be at
- * least 3/4 of the length of in
- * @return the number of bytes written, or a negative value in case of
- * error
+ * @param out      buffer for decoded data
+ * @param in       null-terminated input string
+ * @param out_size size in bytes of the out buffer, must be at
+ *                 least 3/4 of the length of in
+ * @return         number of bytes written, or a negative value in case of
+ *                 invalid input
  */
 int av_base64_decode(uint8_t *out, const char *in, int out_size);
 
 /**
- * Encode in base64 the data in in and put the resulting string
- * in out.
+ * Encode data to base64 and null-terminate.
  *
- * @param out_size size in bytes of the out string, it should be at
- * least ((in_size + 2) / 3) * 4 + 1
- * @param in_size size in bytes of the in buffer
- * @return the string containing the encoded data, or NULL in case of
- * error
+ * @param out      buffer for encoded data
+ * @param out_size size in bytes of the output buffer, must be at
+ *                 least AV_BASE64_SIZE(in_size)
+ * @param in_size  size in bytes of the 'in' buffer
+ * @return         'out' or NULL in case of error
  */
 char *av_base64_encode(char *out, int out_size, const uint8_t *in, int in_size);