"DTS going backward" at some conditions

[Andrey Utkin]

When i execute the below command

GST_DEBUG=3 GST_DEBUG_DUMP_DOT_DIR=. gst-launch-1.0 rtspsrc
location=rtsp://media.smart-streaming.com/mytest/mp4:sample_phone_150k.mp4
name=source ! application/x-rtp, media=video ! queue ! rtph264depay  !
mpegtsmux name=mux ! queue ! udpsink host=127.0.0.1 port=1234
source. ! queue ! rtpmp4gdepay  ! mux.

i have such output (note the warnings at bottom)

Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Progress: (open) Opening Stream
Progress: (connect) Connecting to
rtsp://media.smart-streaming.com/mytest/mp4:sample_phone_150k.mp4
Progress: (open) Retrieving server options
Progress: (open) Retrieving media info
Progress: (request) SETUP stream 0
Progress: (request) SETUP stream 1
Progress: (open) Opened Stream
Setting pipeline to PLAYING ...
New clock: GstSystemClock
Progress: (request) Sending PLAY request
0:00:02.247666247 16660 0x7f1f8802b9e0 FIXME                default
gstutils.c:3625:gst_pad_create_stream_id_internal:<fakesrc0:src>
Creating random stream-id, consider implementing a deterministic way
of creating a stream-id
0:00:02.247745775 16660 0x7f1f8802ba30 FIXME                default
gstutils.c:3625:gst_pad_create_stream_id_internal:<fakesrc1:src>
Creating random stream-id, consider implementing a deterministic way
of creating a stream-id
Progress: (request) Sending PLAY request
Progress: (request) Sent PLAY request
0:00:02.737265031 16660 0x7f1f8802b850 WARN         rtpjitterbuffer
rtpjitterbuffer.c:185:rtp_jitter_buffer_set_clock_rate: Clock rate
changed from 0 to 90000
0:00:02.838822152 16660      0x12249e0 WARN         rtpjitterbuffer
rtpjitterbuffer.c:185:rtp_jitter_buffer_set_clock_rate: Clock rate
changed from 0 to 48000
0:00:04.668274799 16660      0x11e54f0 FIXME               basesink
gstbasesink.c:3022:gst_base_sink_default_event:<udpsink0> stream-start
event without group-id. Consider implementing group-id handling in the
upstream elements
0:00:14.416913998 16660      0x12340f0 WARN               mpegtsmux
mpegtsmux.c:1046:mpegtsmux_clip_inc_running_time:<mux:sink_65>
ignoring DTS going backward
0:00:27.417683308 16660      0x12340a0 WARN               mpegtsmux
mpegtsmux.c:1046:mpegtsmux_clip_inc_running_time:<mux:sink_66>
ignoring DTS going backward

These warnings from last lines appear at random periods (and frequency
depends on pipeline config), but not once.
Also the strange thing is that line "buffering XX%" is there all the
time, and constantly rolling from 0% to 100% again and again.

But when i remove queue between muxer and udpsink, such warnings (and
"buffering" line too) are absent. I am not sure if it means there is
no problem in such case, or it just doesn't manifest itself.

Would be great if somebody explained why such thing happens.

-- 
Andrey Utkin