NTP Timestamp in DeepStream

DeepStream 5.0 supports setting NTP timestamps per frame. Calculated NTP timestamp will be available in ntp_timestamp field of NvDsFrameMeta.

DeepStream calculates NTP timestamps in 2 ways.

1. Host system time as NTP timestamp: when the frame is received by the NvStreamMux plugin in the DeepStream pipeline.

To attach host system time as NTP timestamp, user needs to set "attach-sys-ts" to TRUE on nvstreammux.

In DeepStream reference app this can be done by setting "attach-sys-ts-as-ntp" config parameter to 1 in [streammux] group of the application configuration file.

For this method user must synchronize host system to NTP clock.

2. NTP timestamp when attached at RTSP source: This is supported only if RTSP sources send RTCP Sender Reports (SR).

To configure the pipeline to attach these timestamps:

• user needs to set "attach-sys-ts" to FALSE on nvstreammux. In deepstream reference app this can be done by setting "attach-sys-ts-as-ntp" config parameter to 0 in [streammux] group of the application configuration file

• After creating an "rtspsrc" element or an "uridecodebin" element, application must call configure_source_for_ntp_sync() function and pass the pointer to the GstElement to this API.

(Refer to create_rtsp_src_bin() in deepstream_source_bin.c file) The API will internally configure the pipeline to parse sender report and calculate NTP timestamps for each frame.

• Make sure RTSP source can send RTCP Sender Reports.

This can be verified by starting streaming from the source on a host and viewing the packets in a tool like wireshark/tshark on the same host to confirm the presence of Sender Reports (SR).

Example method to check if RTSP source sends RTCP sender reports using a tool like tshark. We assume RTSP source has IP address 192.168.1.100.

1. Install tshark on a host

sudo apt-get install tshark

2. Find the host network interface that would be receiving the RTP/RTCP packets.

$ sudo tshark -D

...

eno1

...

3. Start the monitoring using tshark tool. Replace the network interface and source IP as applicable.

$ sudo tshark -i eno1 -f "src host 192.168.1.100" -Y "rtcp"

4. On the same host, start streaming from the RTSP source only after starting the monitoring tool. Any client may be used.

$ gst-launch-1.0 rtspsrc location= <RTSP URL e.g. rtsp://192.168.1.100/stream1> ! fakesink

5. The output of the tshark monitoring tool should have lines containing "Sender Report Source description". Sample output as follows:

6041 10.500649319 192.168.1.100 → 192.168.1.101 RTCP 94 Sender Report Source description