AJA HELO Plus SRT gateway setup with Callaba
Written by Iurii Pakholkov
Founder of Callaba. Building cloud video tools for SRT, RTMP, WebRTC, NDI, live routing, monitoring, recording, and production workflows.
Release: Callaba 8.4
AJA HELO Plus SRT setup is a direct encoder-to-gateway workflow. Feed SDI or HDMI into HELO Plus, configure one of its stream outputs as SRT Caller, and send that stream to a Callaba SRT Listener. Callaba then receives the contribution feed and can show preview, recording, restreaming, routing, playback, multiview, and API workflows as parallel downstream uses.
Quick answer
To use AJA HELO Plus with SRT, set HELO Plus as the SRT Caller and send the stream to a cloud SRT Listener. In this guide, Callaba works as the SRT gateway, receiver, monitor, recorder, and routing layer.
AJA HELO Plus sends one SRT contribution feed into Callaba Gateway. After ingest, Callaba can preview, record, route, restream, and play back the same source in parallel; these are not mandatory sequential setup steps.
- AJA HELO PlusSDI/HDMI in · SRT caller
- Callaba GatewaySRT listener · cloud receiver
- Preview
- Record
- Restream
- Route
- Playback
- API
What this setup does
HELO Plus is a compact H.264 streaming and recording encoder with SDI and HDMI I/O. AJA lists SRT caller mode and listener mode, RTMP, RTMPS, RTSP, HLS, and RTP-TS/UDP-TS for this model. For contribution to Callaba, the cleanest path is HELO Plus SRT caller to a Callaba SRT listener.
This distinction matters for common search phrases. In a normal HELO Plus SRT gateway workflow, HELO Plus is not the cloud receiver. Callaba is the HELO Plus SRT receiver, the HELO Plus SRT to cloud endpoint, and the practical AJA HELO Plus SRT server on the internet. HELO Plus listener mode exists, but I treat it as an advanced fallback because the venue side must accept an inbound UDP connection.
Do not plan AJA HELO Plus as a native NDI source. Official HELO Plus specifications do not list native NDI, SMPTE ST 2110, HEVC/H.265, 4K/UHD encoding, bonding, or a required vendor cloud receiver layer for this model.
Recommended workflow
Use HELO Plus Stream 1 or Stream 2 as an outbound SRT Caller. Create an SRT server in Callaba, choose a UDP port, and copy the public host, port, passphrase, encryption strength, and Stream ID if your routing policy uses one. Start with one encoder output, then add the second output only after the first one is stable.
If you reverse the roles and use HELO Plus as SRT Listener, the device side needs a public IP, UDP port forwarding, firewall permission, or a tested NAT traversal plan. That is why I prefer caller mode for most internet contribution workflows.
Before you start
Confirm the installed HELO Plus firmware before the event. SRT Listener mode and the SRT Caller Stream ID parameter belong to the HELO Plus v2.1 firmware generation. Also confirm that the source format, H.264 bitrate, AAC audio, and network uplink fit the event.
- Open HELO Plus Web UI and confirm the SDI or HDMI source is locked.
- Confirm outbound UDP from the venue to the Callaba public address.
- Keep Stream ID and passphrase exactly matched; case, whitespace, trailing spaces, and copied newlines matter.
For difficult handshake failures, check SRT library or major-version compatibility on both sides. On the device side, use HELO Plus firmware release notes or AJA support information. On the Callaba side, check server build information, release notes, or support information.
Create the Callaba ingest
In Callaba, open the SRT server area and create a listener for the event. Choose a UDP port that is open on the cloud firewall. If the workflow uses encryption, set AES-128 or AES-256 and a passphrase. If you use Stream ID for routing, create the exact Stream ID that HELO Plus will send.
- Open
- SRT servers
- Create
- Listener on UDP port
- Success
- Incoming bitrate and preview
Success looks simple: the Callaba SRT server moves from waiting to connected, incoming bitrate appears, connection uptime starts, and preview/audio meters show the program feed.
Configure HELO Plus
Open the HELO Plus Web UI, choose Stream 1 Output or Stream 2 Output, and select SRT Caller as the stream type. Fill the SRT Destination URL with the Callaba public host and UDP port. Then match SET Caller Stream ID, SRT Caller Security, and SRT Caller Encryption Passphrase if those are used in Callaba.
For a first internet test, use H.264 High or Main profile if your downstream decoder supports it. Practical starting bitrates are 2.5-4 Mb/s for 720p, 4-6 Mb/s for 1080p30, and 6-8 Mb/s for 1080p60. If HELO Plus exposes GOP or keyframe settings in your firmware, a 2-second keyframe interval is a good first test for monitoring and restreaming.
If the installed firmware exposes an SRT latency field, start around 250-500 ms for internet contribution and lower it only after packet loss, RTT, and retransmits are stable.
Settings table
| Where | What to do / field to fill | First-test value | Why / check |
|---|---|---|---|
| Callaba | Create SRT server and choose UDP port | 9000 or another open event port | Server should wait for an incoming caller. |
| Callaba | Set encryption strength | AES-128 or AES-256, matching HELO Plus | A mismatch can stop the handshake. |
| Callaba | Set passphrase if encryption is enabled | Paste exactly | Case, whitespace, and trailing newline are significant. |
| Callaba | Set Stream ID or routing rule if used | Event-specific path or token | Must match HELO Plus SET Caller Stream ID. |
| HELO Plus Stream output page | SRT Destination URL | Callaba public host and UDP port | Callaba should show a new connection attempt. |
| HELO Plus Stream output page | SET Caller Stream ID | Same string used in Callaba | Do not add spaces before or after the value. |
| HELO Plus Stream output page | SRT Caller Security | Same AES choice as Callaba | Keep both sides identical. |
| HELO Plus encoder settings | Video bitrate | 1080p30: 4-6 Mb/s to start | Adjust to uplink headroom and production quality. |
Monitoring
Monitor both endpoints during rehearsal. In Callaba, watch incoming bitrate, RTT, packet loss, retransmits, connection uptime, preview, and audio meters. On HELO Plus, watch the Web UI status page, streaming state, front-panel streaming indicators, and audio meters.
A stable setup should hold a steady bitrate with low retransmit pressure and no recurring reconnects. If preview works but audio is missing, check HELO Plus input audio selection and the downstream audio meters separately.
Recording and playback
HELO Plus can record a local backup to SD, USB, SMB, or NFS storage while streaming. Callaba recording is a separate cloud-side option after ingest. Treat these as parallel backups, not as a required sequence.
PlayToStream is a purchasable HELO Plus option for streaming previously recorded material from storage. It is not required for live SRT contribution into Callaba. If you need more than the standard stereo configuration, confirm the 4-channel audio option and test the target protocol before production.
Troubleshooting
| Symptom | Check in Callaba | Check on HELO Plus | Likely fix |
|---|---|---|---|
| No connection | Listener running, UDP port open, no wrong server selected | SRT Destination URL, DNS, gateway, stream started | Open firewall/NAT for outbound UDP and confirm host:port. |
| Handshake fails | Encryption, passphrase, Stream ID, server logs | SRT Caller Security, passphrase, SET Caller Stream ID | Re-type values manually; remove trailing spaces and copied newlines. |
| Connects, then drops | RTT, loss, retransmits, bitrate spikes | Encoder bitrate, source frame rate, uplink quality | Raise SRT latency, lower bitrate, or move to a better network. |
| Video works, no audio | Preview audio meters and recording audio track | Embedded SDI/HDMI or analog input selection and meters | Select the correct audio input and confirm AAC stereo output. |
| NDI or HEVC expected | Confirm ingest is actually SRT or RTMP | Check exact HELO Plus specs, not another AJA model | Use SDI/HDMI conversion or a separate bridge if NDI is required. |
| RTSP path fails | Use SRT ingest where possible | Remember RTSP is a pull/client access mode | Use RTSP only for local viewing or a tested bridge, not as the main WAN path. |
Official references
These are the most useful references for this exact setup.
Vendor references
- AJA HELO Plus product page and technical specifications
- AJA HELO Plus support and downloads
- AJA HELO Plus Manual v2.1r3
- AJA HELO Plus v2.1 SRT Stream ID and Listener mode announcement
Protocol references
Callaba resources
FAQ
How do I use AJA HELO Plus with SRT?
Use HELO Plus as SRT Caller and send the stream to a Callaba SRT Listener. Match host, UDP port, Stream ID, encryption strength, passphrase, and bitrate.
Should HELO Plus be SRT caller or listener?
Use caller mode by default. HELO Plus SRT listener mode is useful only when your network design allows inbound UDP to the device or venue.
Is HELO Plus the SRT receiver?
Not in the recommended cloud contribution workflow. HELO Plus is the encoder and caller; Callaba is the receiver/listener and gateway.
Can HELO Plus send RTMP or RTMPS instead?
Yes. AJA lists RTMP and RTMPS for HELO Plus. I would use RTMP/RTMPS as a fallback when SRT is not accepted by the receiving system.
Does AJA HELO Plus support native NDI or HEVC/H.265?
Official HELO Plus specifications list H.264/MPEG-4 encoding, not HEVC/H.265. Native NDI and SMPTE ST 2110 are not listed for this model.
Why does the SRT Stream ID or passphrase fail?
Most failures are exact-string mismatches. Check capitalization, leading or trailing spaces, copied newlines, wrong AES choice, and incompatible SRT versions.
Next steps
Build the path in a controlled network first, then repeat the same test on the venue uplink. Save the working HELO Plus preset, document the Callaba server name and UDP port, and rehearse start/stop behavior. If the event is important, record locally on HELO Plus and in Callaba so you have two independent backups.
Try Callaba Gateway with AJA HELO Plus SRT
Create an SRT server in Callaba, send the device feed to the gateway, and check the received stream. After ingest is stable, use Callaba outputs for preview, recording, restreaming, multiview, playback, routing, or API workflows as parallel downstream options.