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lavu: add av_gettime_relative()

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These functions are using the POSIX clock_gettime() function with the
CLOCK_MONOTONIC clock id. If these are not present on the targeted
platform, the new functions will fallback on using the original realtime functions
av_gettime() and av_usleep().

Monotonic support can be added on other platforms with their
equivalent native system API eventually if possible.

Whenever time is requested to measure relative time, the monotonic clock,
when available, is superior to the system realtime clock because it is
not affected by discontinuous jumps in the system time

In a future step, offering the flexibility to let the user choose between
rt and monotonic clock for avdevices packets will be investigated.

It is very easy to experience the issues that this patch attempt to address
by rewinding back in the past the system time while ffmpeg is running.

this is breaking the ffmpeg report printing (ffmepg.c:print_report()) and
the the rate emulator functionality (-re) without the patch.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Olivier Langlois
2014-05-12 16:26:37 -04:00
committed by Michael Niedermayer
parent a7320c1574
commit 0eec06ed87
4 changed files with 39 additions and 1 deletions
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doc/APIchanges
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@@ -15,6 +15,9 @@ libavutil: 2012-10-22
API changes, most recent first:
2014-05-xx - xxxxxxx - lavu 52.84.100 - time.h
Add av_gettime_relative() av_gettime_relative_is_monotonic()
2014-05-xx - xxxxxxx - lavf 55.17.0 - avformat.h
Add AVMFT_FLAG_BITEXACT flag. Muxers now use it instead of checking
CODEC_FLAG_BITEXACT on the first stream.