lavu: add av_usleep() function

This function implements a delay using the first available
of the following functions:

- nanosleep()
- usleep()
- Sleep() (Windows)

The conditional #includes in time.c are simplified by including
unistd.h and windows.h whenever they are available rather than
having these lines triggered by specific functions.

Signed-off-by: Mans Rullgard <mans@mansr.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/libavutil/time.h b/libavutil/time.h
index 2ee7e08caf..b01a97d770 100644
--- a/libavutil/time.h
+++ b/libavutil/time.h
@@ -26,4 +26,14 @@
  */
 int64_t av_gettime(void);
 
+/**
+ * Sleep for a period of time.  Although the duration is expressed in
+ * microseconds, the actual delay may be rounded to the precision of the
+ * system timer.
+ *
+ * @param  usec Number of microseconds to sleep.
+ * @return zero on success or (negative) error code.
+ */
+int av_usleep(unsigned usec);
+
 #endif /* AVUTIL_TIME_H */