Unexpected variable latency in interlaced mode

[slaigre]

Hi!

I noticed that the transmission latency is not predictable when transmitting a 1080i50 stream (also reproducible with 1080i59.94) using the TxSt20PipelineSample.

I sometimes observe a latency of approximately 542 lines early (~19 ms) :

And other times I observe a latency of approximately 21 lines late (~0.736 ms) :

The latency is measured using a Telestream PRISM.

This issue does not occur in progressive mode.

I can reproduce the issue using the following command:

sudo ./build/app/TxSt20PipelineSample  -p_port XXXXXXXXXX -p_sip AA.BB.CC.DD  -udp_port 1234 -p_tx_ip WW.XX.YY.ZZ -payload_type 96 -interlaced -fps 50  -ptp

The issue is also reproducible with RxTxApp using the following JSON configuration:

{
    "interfaces": [
        {
            "name": "XXXXXXXXXX",
            "ip": "AA.BB.CC.DD"
        }
    ],
    "tx_sessions": [
        {
            "dip": [
		"WW.XX.YY.ZZ"
            ],
            "interface": [
                0
            ],
            "st20p": [
                {
                    "replicas": 1,
                    "start_port": 1234,
                    "payload_type": 96,
                    "width": 1920,
                    "height": 1080,
		    "interlaced": true,
                    "fps": "p50",
                    "device": "AUTO",
                    "input_format": "YUV422PLANAR10LE",
                    "transport_format": "YUV_422_10bit",
                    "st20p_url": "testyuv"
                }
            ]
        }
    ]
}

RxTxApp output log:
RxTxApp_log.txt

MTL version : main branch 982e2ea
OS : Ubuntu 22.04.5 LTS

Status report:
system_info.txt
kernel_log.txt

Thank you in advance for your feedback.

[Sakoram]

Hi, it looks like your transmitter is not synchronized with the receiver.
Please try to:

1. Make sure there is PTP master clock in your network.
2. Run RxTxApp with --ptp parameter or run ptp4l and phc2sys in your system to synchronize the system clock (RxTxApp uses system clock without --ptp)

[slaigre]

Thank you for your feedback.
Streamer and receiver are synchronized using ptp4l/phc2sys, this is ok. Using the --ptp with RxTxApp gives the same behaviour (542 lines adv / 21 lines delay).
By synchronizing another server to PTP with the same grandmaster, it's ok using the nvidia rivermax sdk.
Thank you in advance.

[Sakoram]

We have automated tests that should catch this, but possibly they are faulty. I will investigate that and will let you know if I can reproduce your issue.

[Sakoram]

I confirm that I see some issues related to latency when video in interlaced mode. I will look into this soon.

[Sakoram]

Hi, could you check if this issue occurs on this branch: #1649? I haven't been able to reproduce any latency issues on this branch. It's currently under review. I hope to merge it soon.