splitmuxsink, issues with max-size-time and e xact duration

Hi. 
 
I found very strange issue with splitmuxsink and it’s  max-size-time property, namely
given n sec. for desired duration, it’s actual duration would be n-2 sec.  Initially I’ve discovered this
issue while testing hand-coded pipeline, but then desided to reproduce the issue with gst-launch
and observed the very same behaviour. Given 
gst-launch-1.0 -e -v rtspsrc buffer-mode=0 add-reference-timestamp-meta=true  location=rtsp://user:pass@ip_addr/onvif/media?profile=Profile1 ! rtph264depay ! h264parse ! splitmuxsink location="d:\\video_files\\video_%02d.mp4" max-size-time=10000000000
(note, max-size-time=10000000000 is 10 sec in nanoseconds)
the actual duration of files will be 8 sec.
Same for 7→ 5, 5→ 3, and so on. So, it seems to be the pattern — set for n secodns, receive for n-2 seconds.
Is it ok or maybe I miss something? I don’t think that it depends on rtps source.
 
Thanks in advance.
 
Here some initial seesion info:
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: latency = 2000
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: ntp-sync = false
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: rfc7273-sync = false
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: add-reference-timestamp-meta = true
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: ntp-time-source = ntp
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: drop-on-latency = false
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: max-rtcp-rtp-time-diff = 1000
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: max-ts-offset-adjustment = 0
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: buffer-mode = none
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc1: timeout = 5000000000
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc1: caps = application/x-rtp, media=(string)video, payload=(int)97, clock-rate=(int)90000, encoding-name=(string)H264, packetization-mode=(string)1, profile-level-id=(string)4D00000000000000, sprop-parameter-sets=(string)"Z00AH52oFAFum4CAgIE\=\,aO48gA\=\=", a-framerate=(string)15, ssrc=(uint)3053121902
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc2: caps = application/x-rtcp
Progress: (request) SETUP stream 1
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc3: timeout = 5000000000
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc3: caps = application/x-rtp, media=(string)audio, payload=(int)0, clock-rate=(int)8000, encoding-name=(string)PCMU, encoding-params=(string)1, ssrc=(uint)2174462030
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc4: caps = application/x-rtcp
Progress: (open) Opened Stream
Setting pipeline to PLAYING ...
New clock: GstSystemClock
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstRtpBin:manager: buffer-mode = none
Progress: (request) Sending PLAY request
Redistribute latency...
Redistribute latency...
Progress: (request) Sending PLAY request
Redistribute latency...
Redistribute latency...
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc1: caps = application/x-rtp, media=(string)video, payload=(int)97, clock-rate=(int)90000, encoding-name=(string)H264, packetization-mode=(string)1, profile-level-id=(string)4D00000000000000, sprop-parameter-sets=(string)"Z00AH52oFAFum4CAgIE\=\,aO48gA\=\=", a-framerate=(string)15, ssrc=(uint)3053121902, clock-base=(uint)2632806877, seqnum-base=(uint)14666, npt-start=(guint64)0, play-speed=(double)1, play-scale=(double)1, onvif-mode=(boolean)false
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc3: caps = application/x-rtp, media=(string)audio, payload=(int)0, clock-rate=(int)8000, encoding-name=(string)PCMU, encoding-params=(string)1, ssrc=(uint)2174462030, clock-base=(uint)661265319, seqnum-base=(uint)53364, npt-start=(guint64)0, play-speed=(double)1, play-scale=(double)1, onvif-mode=(boolean)false
Progress: (request) Sent PLAY request
/GstPipeline:pipeline0/GstRTSPSrc:rtspsrc0/GstUDPSrc:udpsrc1.GstPad:src: caps = application/x-rtp, media=(string)video, payload=(int)97, clock-rate=(int)90000, encoding-name=(string)H264, packetization-mode=(string)1, profile-level-id=(string)4D00000000000000, sprop-parameter-sets=(string)"Z00AH52oFAFum4CAgIE\=\,aO48gA\=\=", a-framerate=(string)15, ssrc=(uint)3053121902, clock-base=(uint)2632806877, seqnum-base=(uint)14666, npt-start=(guint64)0, play-speed=(double)1, play-scale=(double)1, onvif-mode=(boolean)false
 
 
 
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С Уважением,
Шаров Антон