Understanding Dashboard input alerts

Sometimes Spalk's ingest server will detect an error with the input stream we are receiving. This article outlines the warnings you may see displayed, and remediation steps.

WARNING: We haven't yet been able to analyse the packets from this stream

This is a warning to let you know we have been unable to inspect the ingest stream internals and provide analysis or other specific warnings about the contents of the input. This is an important warning as we are unable to provide any more information about the contents of the stream. If there are no problems with the input stream, your commentators and outputs should still be able to start successfully, and the warning should resolve in a few minutes. If it does not resolve please try stopping and starting the input signal to Spalk. Note this will disconnect all commentators and outputs. If that does not resolve the issue, please contact a Spalk representative. 

ALERT: There is no video or audio detected in this events ingest stream

ALERT: There is no video detected in this events ingest stream

Spalk requires both video and audio tracks on the ingest stream for our synchronisation logic to work as expected, so this alert is displayed when one or both of those are missing. We will show a warning if there is no video Packetised Elementary Stream (PES) present in the Transport Stream or if we detect a video PES with missing metadata. In order to remedy this, please check your encoder settings to ensure you are sending Spalk a video PES - this is sometimes listed as a video PID. Note: This alert is currently only displayed for SRT events. 

ALERT: We are failing to decode the input stream. Please check the input transport stream

Upon receiving an input stream, the ingest server will transcode it into different resolutions for the commentator to view in the Studio (360p, 480p, 720p or 1080p). If the ingest server is unable to create the transcoded streams, then this error will be displayed.

This warning is displayed for one of two reasons.

1. The server cannot decode the input Transport Stream (TS). This will mean at least one video resolution in Commentator Studio is unable to play successfully. The commentator will see a black or frozen screen. Please double check your encoder settings to ensure you are sending Spalk a TS with valid encoder settings. If you need to validate your encoder settings are correct, please contact a Spalk representative.

2. The ingest server can decode the input, but is failing to transcode the input stream at the incoming framerate (for example Spalk is processing 20 fps of a 25fps stream). In this case a commentator will see choppy, or "slow-motion" playback. This may be solved by resetting the encoder that is streaming to Spalk. If this does not resolve after stopping and starting the input signal to Spalk, please double check your encoder settings are correct. If you need to validate your encoder settings are correct, please contact a Spalk representative.

ALERT: The input PIDs in your audio configuration do not match the incoming stream. Please go to the Audio Config tab to fix this.

If the audio configuration contains input PES packet identifiers (PIDs) that are not present on the incoming Transport Stream, then the processes trying to access that PID will fail and either cause transcode errors (the above warning would also be displayed) or the return feed would fail to be created. Remedy this by updating the audio configuration with the correct PIDs.

ALERT: At least one of your audio streams has a bitrate that is considered too low, this may cause issues in the broadcast.

This alert shows when the Transport Stream contains an audio Packetised Elementary Stream (PES) with a bitrate less than 12kbps. If Spalk is required to insert either commentator audio or copy another audio PES's packets into the PES with the low bitrate, audio degradation will occur. In order to remedy this, you will need to increase the bitrate of the problematic audio PES.

ALERT: The NULL packet bitrate is ... and is considered too low, please increase it to at least 128kbps. This may cause output audio degradation.

In a Constant Bitrate (CBR) transport stream the MPEG-TS multiplexer will insert NULL packets to preserve a strictly constant bitrate when the audio and video PES bitrates are varying. When there are not enough NULL packets it can indicate that the overall bitrate is too low, and leave no space for Spalk to insert/replace audio streams. This warning will only show up on CBR SRT events. Click here for more information https://spalk.zendesk.com/hc/en-us/articles/7037039176463 

ALERT: This appears to be a Variable Bitrate (VBR) transport stream. No NULL packets detected.

As above, a Constant Bitrate (CBR) transport stream should contain NULL packets. If we are unable to detect any NULL packets, this stream is very likely to be produced as VBR. This causes issues with timing and replacing streams. This warning will only show up on CBR SRT events. Click here for more information. https://spalk.zendesk.com/hc/en-us/articles/7037039176463 

ALERT: We are detecting high ingest clock skew between the stream input and our reference clock. This will cause quality issues downstream. This is usually fixed by an encoder reboot, if the issue persists you may have issues with the encoder clock.

For MPEGTS over SRT streams Spalk expects to receive Program Clock References (PCRs) at least every 40ms with clock frequency 27MHz. RTMP stream clock references should be present on every video frame, with a 1KHz clock frequency. Every time we receive a clock reference, we also measure it against our own internal reference clock. If the encoder clock is running substantially faster or slower than the reference clock (and the commentator's audio encoder clock), then the audio quality will be degraded. This is known as high skew. This can often be solved by rebooting the encoder and is usually due to an "unlocked" encoder, incorrect clock synch configuration or a faulty clock chip. If you have rebooted the encoder and the warning is still present, please try another encoder and contact the manufacturer of the problematic one.