* Wrapper to work around the lack of mkstemp() on mingw.
* Also, tries to create file in /tmp first, if possible.
* *prefix can be a character constant; *filename will be allocated internally.
- * @return file descriptor of opened file (or -1 on error)
+ * @return file descriptor of opened file (or negative value corresponding to an
+ * AVERROR code on error)
* and opened file name in **filename.
* @note On very old libcs it is necessary to set a secure umask before
* calling this, av_tempfile() can't call umask itself as it is used in