diff --git a/libavformat/internal.h b/libavformat/internal.h
index b746c1dd5c..232b40b253 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -167,6 +167,17 @@ int ff_get_v_length(uint64_t val);
  */
 void ff_put_v(ByteIOContext *bc, uint64_t val);
 
+/**
+ * Read a whole line of text from ByteIOContext. Stop reading after reaching
+ * either a \n, a \0 or EOF. The returned string is always \0 terminated,
+ * and may be truncated if the buffer is too small.
+ *
+ * @param s the read-only ByteIOContext
+ * @param buf buffer to store the read line
+ * @param maxlen size of the buffer
+ * @return the length of the string written in the buffer, not including the
+ *         final \0
+ */
 int ff_get_line(ByteIOContext *s, char *buf, int maxlen);
 
 #define SPACE_CHARS " \t\r\n"