[FFmpeg-devel] [PATCH] Use monotonic clock for measuring reltime.
LANGLOIS Olivier PIS -EXT
olivier.pis.langlois at transport.alstom.com
Wed Apr 2 20:05:01 CEST 2014
> -----Original Message-----
> From: ffmpeg-devel-bounces at ffmpeg.org [mailto:ffmpeg-devel-
> bounces at ffmpeg.org] On Behalf Of Nicolas George
> Sent: Wednesday, April 02, 2014 12:15 PM
> To: FFmpeg development discussions and patches
> Subject: Re: [FFmpeg-devel] [PATCH] Use monotonic clock for measuring
> Le tridi 13 germinal, an CCXXII, Don Moir a écrit :
> > The wall time can change by a second or seconds forward or backward
> > depending on automated clock updates and user setting.
> They are bogus settings. Modern operating systems can smooth the
> correction over a period of time to update the clock by a small amount.
from man ntpdate:
Time adjustments are made by ntpdate in one of two ways. If ntpdate determines
the clock is in error more than 0.5 second it will simply step the time by
calling the system settimeofday() routine. If the error is less than 0.5 secâ
onds, it will slew the time by calling the system adjtime() routine. The latter
technique is less disruptive and more accurate when the error is small, and
works quite well when ntpdate is run by cron every hour or two.
settimeofday() or clock_settime() cause jumps, adjtime() will slow down or speed it up to correct the clock.
> > Can change during daylight savings time switch over by an hour as well.
It depends. You have the option to store the system time in the RTC (hardware clock) either as UTC or local time in Linux. Setting RTC time in local time isn't advised but may be required if dual booting with Windows. When having DST change, you either let the other OS correct the RTC time or you can manually fix it.
I have 0 Windows installation around me so I am not sure but I would not totally rule out that manual DST management can have effect on system time.
inspect /etc/adjtime content to find out how your RTC is configured or see
for more info on the topic.
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