How to map specific channels and tracks from an input with multiple audio tracks to the output

When dealing with broadcast transport streams, one typically encounters the scenario where there are multiple audio tracks. One of the key features of Spalk is channel/track mapping, which allows you to map input channels or tracks to specific output channels or tracks. In this article, we will explain how to use channel/track mapping to ensure commentary is mixed with the correct input, and placed in the correct track on the output.

It's important to note that you can either map whole tracks or individual channels, but cannot use a combination of both. To mimic the whole track behaviour in channel mode, map every input channel to every channel in the output track.

Mapping By Tracks

To map whole tracks from input to output by Packet Index (PID), follow these steps:

1. Create the input track by clicking the "+" button beside the input labelled SRT. You will need to specify a label for the track (e.g. International Sound) and the PID of the input track in hexadecimal. If you don't know the input PID, check the "Stream Status" dropdown while the event is live to view the incoming tracks (PIDs) on your stream.
2. Create an output track by clicking the "+" button beside "Output Track". You will need to by give it a label (eg En-mix), and select the output PID. This is the PID that the output will be mixed onto.
3. Map input tracks to output tracks by selecting the radio button on the left, and clicking on the output on the right.
4. If you wish to mix commentary teams into the output, map commentary teams to output tracks by selecting the radio button on the left of the team name you wish to mix, and clicking on the output on the right.
5. Click the Save button once your input and output mapping is set up correctly.

To remap clean PIDs, do not add a commentary team to the output track. This is useful when you want to move a track, e.g. International Sound from Track 1 to Track 2.

Output tracks without input tracks mapped will have no background sound mixed.

Mixing International Sound with 2 different commentary teams. In this example international sound (IS) is present on PID 0x1010, and we replace it with a full stereo mix of commentators + IS on that PID for output. Both teams can be mapped to the same PID, as they will produce separate output Transport Streams.

Mapping By Channel

To map inputs to outputs by individual channel, select the "Channels" radio button at the top. This is useful when you have dual mono tracks

1. Create the input track by clicking the "+" button beside the input labelled SRT. You will need to specify a label for the track (e.g. International Sound) and the PID of the input track in hexadecimal. If you don't know the input PID, check the "Stream Status" dropdown while the event is live to view the incoming tracks (PIDs) on your stream.
2. Create an output track by clicking the "+" button beside "Output Track". You will need to by give it a label (eg Isolated English), and select the output PID. This is the PID that the output will be mixed onto.
3. Map input channels to an output by clicking the channel on the input, and clicking on the output channel on the right.
4. Repeat step 3 until you have your desired configuration.
5. Click the Save button once your input and output mapping is set up correctly.

Mapping split audio channels to allow a downstream taker to mix it themselves. In this example international sound is present on PID 0x1010, and we replace it with a dual mono, with IS mono mix on Left channel, and Commentator mono mix on Right channel.

Important Notes:

• The channel mapping is set up when the commentator/output connects for the first time. If you need to make changes, you need to reset the team's media workflow, or stop and start the input SRT stream.
• If the specified input PID does not exist in the incoming stream, the commentator/output will fail to connect on startup.
• If the output PID already exists in the incoming stream, Spalk will replace it in the stream.
• If the output PID does not exist in the incoming stream, Spalk will insert it into the stream. This will not work with VBR, as there is no "spare" NULL data in the stream to replace with the new stream. This will mean the commentator is not present in the output streams.
• Any SRT, or MediaConnect outputs for a team with a channel mapping applied will contain the full input stream, with the commentator mixed with and onto the tracks specified.
• Any RTMP outputs for a commentary team with a channel mapping applied will only contain the video and the specific audio track that the commentator is mixed on.
• If you don't specify any channel mapping, the default behaviour is to mix every commentary team onto the lowest PID detected, and replace that PID with the mix. This is typically channels 1&2.

Limitations:

• You can only map commentators to one output track at a time.
• You can only map a single commentary team to each output track
• You can only map a single input track to each output track

Mapping channels or tracks in Spalk is a useful tool for integrating remote commentary into streams with multiple audio tracks. We hope this guide has provided you with a comprehensive understanding of the process involved in channel/track mapping in Spalk. If you encounter any issues or have any questions, don't hesitate to contact our support team for assistance.