Overview
Captioning adds live captions and translations to your Castr live streams. You create a captioning flow, pick a stream, choose languages, and captions appear in the player within about a minute.
Beta: Captioning is in Beta and available on all Castr plans during this period. Settings and options may change when it leaves Beta.
Find it under Advanced → Captioning in the dashboard sidebar.
Each live stream gets one captioning flow.
Your included captioning hours and the next reset date are shown next to the page title.
Already have a SyncWords account? You can connect it instead of using Castr's included hours.
Before you start
You need three things in place before creating a captioning flow:
A Castr live stream to receive the captioned video. It can be offline while you set things up.
An encoder that can push SRT (OBS, vMix, Wirecast, hardware encoders). The flow gives you an SRT ingest URL to send your feed to.
Captioning hours on your plan, or your own SyncWords account connected.
Pick the stream carefully: it can't be changed after the flow is created. To switch streams, delete the flow and make a new one.
Set up captions step by step
Setup takes two dialog steps. After that, you start captions and point your encoder at the SRT URL Castr gives you.
1. Open Captioning
In the sidebar, go to Advanced → Captioning and click New captioning.
2. Pick your stream (Step 1 of 2)
Search for or select the Castr live stream that should receive the captioned video, then click Next. You can't change the stream later.
3. Choose languages and caption style (Step 2 of 2)
Spoken language: the language people speak on the stream. This becomes the original caption track.
Caption languages: click Add language to add translations, up to 4 languages in total. Each translated language has an engine picker: Auto (recommended), Google, DeepL or Gemini. Languages that Teletext can't display (for example Amharic) are greyed out.
Caption position: Bottom or Top of the picture.
Lines: 1 or 2 subtitle lines on screen at once.
Text colour: White, Yellow, Cyan, Green, Magenta, Red or Blue. Alignment: Left or Center.
Delay buffer: 5–60 seconds (default 30). A higher value gives translations time to keep up, but viewers see the stream that much later.
Speaker labels: marks each change of speaker. Remove filler words: drops "um", "uh" and "er". Both are on by default.
4. Adjust Advanced settings (optional)
Expand Advanced only if you need to change the defaults:
Setting | Options | Default |
Speech engine | Speechmatics, Soniox, Sarvam | Speechmatics |
Region | Automatic, US East, US West, Canada, Sydney, Frankfurt, Ireland | Automatic (nearest to your stream) |
Double height | On / Off: taller letters, each line uses two Teletext rows | On |
Max line length | 20–32 characters per line | 32 (full width) |
Ingest passphrase | 10–79 letters and digits; encrypts the SRT link | None |
If you set a passphrase, enter the same one in your encoder's SRT settings.
Click Create captioning. The flow opens on its own page.
5. Start captions
In Go live with captions → 1 Start captions, choose a Duration (15 min or 1 hour, up to your plan's maximum) and click Start captions. The timer counts down from Start, even while your encoder is offline, so start captions just before you go live.
6. Point your encoder at the SRT ingest URL
In 2 Send your encoder here, click Copy next to the SRT ingest URL and paste it into your encoder as an SRT output. The ingest accepts your encoder only once captions are started. Castr sends the captioned video on to your stream, its player and its restream destinations.
You can still change languages and caption style in Caption settings on this page.
How viewers see captions
Captions are carried in the stream as Teletext subtitle tracks (DVB-TXT), one page per language. The spoken language uses page 888 and each translation takes the next page (for example Spanish on 889).
Castr player: caption support is switched on for the linked stream's player automatically. Viewers pick a language with the player's CC button.
Restream destinations: the captioned video is also sent to the stream's restream destinations.
Player preview: the flow page shows a live preview. Use Reload player to refresh it, Open player to open it in a new tab, and Download captions to save the caption text.
Troubleshooting and FAQ
My encoder can't connect to the SRT ingest URL. Captions must be started first; the ingest accepts your encoder only while captions are running. If you set an ingest passphrase, check that the same passphrase is entered in your encoder.
Captions lag behind the speaker. That's the delay buffer at work. Lower it (minimum 5 seconds) for less delay, or raise it if translations are falling behind.
I picked the wrong stream. The stream can't be changed. Delete the flow and create a new one for the right stream.
A language is greyed out. Some languages, such as Amharic, aren't supported in Teletext subtitles and can't be added.
Can I add more than four languages? No. Each flow supports up to 4 caption languages, including the spoken language.
Do captioning hours run out if my encoder is offline? Yes. The duration counts down from the moment you click Start captions, whether or not video is arriving.
Can I use my own SyncWords account? Yes. Click Connect your own account in the banner at the top of the Captioning page.