Understanding and Monitoring SRT Input Health Metrics for Spalk

Spalk's streaming platform uses Secure Reliable Transport (SRT) technology to ensure high-quality, reliable live video delivery. Understanding the SRT input health metrics is crucial for maintaining optimal streaming performance. This article will guide you through the key SRT input metrics, what they mean, and how to respond if these metrics indicate potential issues.

You can find input health metrics on your Spalk Dashboard under the Stream Status dropdown for SRT events.

Ingest Packet Loss

Ingest Packet Loss is a critical metric that shows the health of the data packets received during a stream. It includes several sub-metrics:

1. PktRecvBelated: This metric indicates packets that arrived late. Late packets can lead to interruptions in the stream.

2. PktRecvLoss: This shows the number of lost packets. Lost packets can cause video artifacts or missing content.

3. PktRecvDrop: This metric counts packets that are dropped, possibly due to network congestion or hardware limitations.

4. Packet Sequence Gap: This indicates gaps in the sequence of packets received, indicating discontinuous transmission of some kind. 

Troubleshooting: If any of these metrics are high, it suggests network issues between your encoder or SRT Gateway and Spalk. Consider checking your uplink network connection, using a wired connection if possible, and ensuring your streaming setup meets the recommended specifications. It can also indicate hardware overloading, so check the appliance for high CPU/GPU/Memory/Disk usage. Finally if your other network metrics indicate high RTT or jitter, you can try increasing the SRT latency to accomodate problems in the connection

Ingest Packet Errors

These errors can significantly impact the quality of your stream:

1. Transport Error Indicator: This error occurs at the transport stream level, often due to signal degradation at an upstream appliance.

2. Continuity Counter Error Count: This error indicates problems in the sequence of MPEG-TS packets in the incoming stream, which can lead to glitches in the stream.

Troubleshooting: High values in these metrics typically point to issues with the transmission source, network link or signal interference. If you don't see any Ingest Packet Loss in other charts, check the stream source upstream. You would expect Continuity Counter (CC) errors if there is packet loss between upstream and Spalk's SRT servers.

Ingest RTT (milliseconds)

Round-Trip Time (RTT) measures the time taken for a packet to be sent from upstream, to Spalk and back again. This metric is crucial in understanding the latency of your network connection to Spalk.

Troubleshooting: A high RTT can be caused by a slow network or a long-distance between the sender and receiver. To decrease RTT, try optimizing your network path or using a server closer to your location. We recommend that the Ingest Latency (see below) is configured to at least 3x the Ingest RTT.

Ingest Bitrate

This represents the rate at which data is being transferred. It's a direct indicator of the quality and smoothness of your stream. We strongly recommend using constant bitrate transport streams, which 

Troubleshooting: Low bitrate can lead to poor video quality. Ensure your network can handle the required bitrate for your stream's resolution and frame rate.

[Insert Screenshot Here]

Ingest Latency (SRT latency)

This is the delay introduced by the SRT protocol to buffer the data and ensure reliable transmission.

Troubleshooting: High SRT latency can lead to delays in your stream. If latency is an issue, consider lowering the buffer settings, though this might increase the risk of packet loss. We recommend that the Ingest Latency (see below) is configured to at least 3x the Ingest RTT.

NULL Packet Bitrate

This metric indicates the bitrate of NULL packets in the MPEG-TS stream, which can be used to maintain a constant bitrate.

Troubleshooting: A low or zero NULL packet bitrate suggests that the MPEG-TS multiplexer is running in Variable Bitrate Mode. See here for more information

MPEG-TS Bitrate by PID

This shows the bitrate for each Packet Identifier (PID) in your MPEG Transport Stream. Different PIDs represent different types of data (e.g., audio, video, metadata).

Troubleshooting: Monitor the bitrates to ensure each stream component is transmitting at the expected rate. Significant deviations might indicate issues with specific stream elements.

Regularly monitoring these metrics will help you identify and resolve issues quickly, ensuring a high-quality streaming experience for your audience. If you continue to experience problems despite these adjustments, please contact Spalk’s technical support for further assistance.