Understanding SRT Input Health Metrics

Spalk's streaming platform provides detailed metrics for the Secure Reliable Transport (SRT) input type to ensure high-quality, reliable live video delivery. This guide will help you understand the key SRT input metrics, their significance, 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.

Key Metrics

Metrics are broken down into sections, each reflecting a separate part of the ingest workflow. If you have created your SRT event with Transcode ON, Spalk inserts a Media Live instance to re-encode your input feed, and your metrics will contain the additional Media Live section.

SRT Link

This section displays metrics for the link between you and Spalk. These metrics can help you diagnose connectivity or transport layer issues.

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

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

     b. PktRecvBelated: This metric indicates packets that arrived late. Late packets can lead to interruptions in the stream.
     c. Packet Loss: This shows the number of lost packets. Lost packets can cause video artifacts or missing content.
     d. TotalPktSeqGap: 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.
     
2. Ingest Packet Errors
   
   • Description:
     This metric shows errors that can significantly impact the quality of your stream. It includes several sub-metrics:
     

     a. ContinuityCounterErrorCount: This error indicates problems in the sequence of MPEG-TS packets in the incoming stream, which can lead to glitches in the stream.
     b. MalformedPacketCount: This error occurs at the transport stream level, often due to signal degradation at an upstream appliance.

   • 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.
     
3. Ingest RTT
   
   Description:
   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.
   
4. Ingest Latency (SRT Latency)
   
   Description:
   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.

Media Live

This section displays metrics of a Media Live instance, which Spalk inserts to re-encode your input feed. This section is only displayed if you have created your SRT event with Transcode ON.

1. Network In
   
   
   • Description: The rate at which data is being received by Media Live. This is a direct indicator of the quality and smoothness of your stream.
   • Troubleshooting: If the bitrate is lower than expected, it can lead to poor video quality. Ensure your network can handle the required bitrate for your stream's resolution and frame rate. Consider using a wired connection for stability.
2. Average Input Video Frame Rate
   
   • Description: The average video frame rate received by Media Live each minute.
   • Troubleshooting: Ensure the frame rate is consistent with the expected input. Variations can affect the viewing experience.
3. Minimum Input Video Frame Rate
   
   
   • Description: The minimum video frame rate received by Media Live each minute.
   • Troubleshooting: Drops in frame rate can indicate network or encoder issues. Ensure the encoder system can handle the required frame rate and is not overloaded.
4. Alert Details
   
   
   • Description: Details of any alerts on the MediaLive encoder. No Data indicates no alert logs to show.
   • Troubleshooting: Investigate alert details to diagnose issues. If you are unable to connect the input stream and seeing No Data, it may indicate an error starting the MediaLive encoder. Contact Spalk support if needed.
5. Active Alerts
   
   
   • Description: The maximum number of alerts on the MediaLive encoder that are active each minute.
   • Troubleshooting: High numbers of active alerts may indicate underlying issues with the encoder or input stream. Investigate the specific alerts to diagnose and resolve issues

MPEG-TS Health

This section displays metrics of MPEG Transport Stream internals at the final step of the ingest workflow.

If you have created your SRT event with Transcode ON, this displays internals of the input feed that you have sent to Spalk after it has been re-encoded by MediaLive. If you have created your SRT event with Transcode OFF, this displays internals of the input feed that you have sent Spalk.

1. Ingest Bitrate
   
   
   • Description: 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. See here for more information
   • 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.
2. NULL Packet Bitrate
   
   
   • Description: The bitrate of NULL packets in the MPEG-TS stream, used to maintain a constant bitrate. For CBR streams, 384kbps is ideal, with a minimum of 90kbps.
   • Troubleshooting: A low or zero NULL packet bitrate suggests that the MPEG-TS multiplexer is running in Variable Bitrate Mode.
3. MPEGTS Bitrates by PID
   
   
   • Description: 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.
4. Program Clock Reference (PCR)
   
   
   • Description: Program Clock Reference (PCR) values received by Spalk. These should be constantly increasing values on a 27MHz clock, resetting to zero at 2576980377599. Note: This panel is only active if you have an active commentator or team output.
   • Troubleshooting: This should be a straight line increasing at a rate of 27,000,000 per second. If this line is not straight, or it is increasing at a different rate, there is a problem with the Program Clock Reference in the Transport Stream Spalk is receiving. Please check the encoder that is sending the Transport Stream to Spalk to ensure it is correct.

Regular Monitoring and Troubleshooting

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

By understanding and managing these input metrics effectively, you can maintain optimal streaming performance and deliver a seamless experience to your viewers.